Fluctuating RPM's and shaking

Okay, so I had a full diagnostic done on the truck check for vacuum leaks and evap leaks and blockages they even tested the electrical parts that I have changed so far and the truck is still running exactly the same. I've taken it to two different mechanics who don't know each other and they don't know the other one has worked on the car and both of them seem to think that there's something wrong with the computer because between the work I and they have done every part that it could be has been replaced. I just want to know if I'm missing anything before I have a new computer put into it. The things I've replaced are as following: EGR valve, IAC valve, fuel filter, spark plugs, air filter, TPS sensor, MAF sensor, 02 sensor, intake air temperature sensor, water temperature sensor, distributor with rotor and cap. The idle is not surging what is doing is it's dropping the almost shut off and the engine has to compensate by making it surge so it's not going up and down it's literally just dropping. In trying to bring itself back up when I have my foot on the gas it's not doing it and when I'm driving it it's not doing it. It's when I take my foot off the gas or try to let a tile that it's dropping in trying to shut off. I'm at a loss I just don't want to spend the money on getting a computer if that's not what it is. The second mechanic ran a diagnostic on it and he said that it was giving him random weird codes and it wasn't giving him a distinct when it was just randomly giving him what he called erratic codes that didn't make sense.

Well, initially I tried to find a port for the OBD reader that I have in the ports in the truck didn't match it and my brother-in-law didn't have any attachments for Nissan so we weren't able to pull any codes. That's when they sent it to the mechanic the original mechanic that looked at it said he was getting a code that was pointing to the mass air flow sensor. We told him that we had already replaced the mass airflow sensor and he said that we needed to get an original Nissan sensor because the one we put in there was $20.00 and was generic. So we replaced it with a newer one and it still didn't work. The second mechanic was sent to the did a full diagnostic on it said that he was getting erratic codes and when we asked what that meant he said I wasn't getting a real code. He said he was getting signals to his reader that were erratic and pointing to different places that didn't make sense. I guess he said his readings were all messed up. He didn't really explain it further. The original mechanic has had it four different occasions trying to figure it out. He's put multiple parts in it and he can't figure it out and the mechanic that did the diagnostic tests on it said they tested every part that I and the mechanic put in and if they were all fine. So the only thing to assume from both of the mechanics was that it was the computer that it's not the parts that are feeling but the computer is sending the wrong messages to the parts or vice versa. But I just wanted to make sure if there was any small thing that I overlooked or checked that could be causing this to happen. The mechanic that put the distributor in when you put it in he said that the timing was off by 4. He also said that he raise the idle to make it stay running, but unfortunately we're all at a loss.

You know that's just the thing both places we took it to me and my family are just going by what the mechanics have said but I found it strange that they didn't give us no printed papers that showed anything kind of like smog test do we didn't have no papers with readings on them they didn't make any mention of vacuum being low in certain areas or the fuel trim ratios nothing about percents or anything and I found it odd that they didn't say anything about those if they were running real diagnostic test I would think they would have said something so I performed kind of a homemade smoke test to it incense smoke through the brake booster tube that was going to the engine and I put smoke through it eight or nine times with pressure and it never came out of anywhere so I didn't believe that there was any kind of a vacuum leak so far but something interesting happened today I unplug the mass airflow sensor and for the first time in two months the car stayed at idle after it warmed up and it was completely fine for 20 minutes and when we called and told one of the mechanics what did that mean he gave us two different answers and contradicted himself first he said that they're not supposed to do that then when you unhook the mass airflow sensor it's supposed to die and then the next minute he told us that it's possible for it to stay running in the Nissan brand because they're made that way so I just was going to ask if unplugging the mass airflow sensor makes it run smooth does that mean the mass airflow sensor is bad because to date we put for total in it and it's been doing the same thing with everyone but both mechanics said that they were getting mixed messages that led them to believe that it kept going back to the mass air flow section I was wondering and I asked the mechanic if the wiring to the harness is bad even if the mass airflow sensor is good if there's a short in the wiring and I plug it in could a short in the wiring be making the mass airflow sensor not work and he said that's not the case but I also know that the mass airflow sensor can malfunction from other parts for example if the O2 sensor is bad and it's reading the mixture is different than it actually is it could signal the mass airflow sensor to pulling more or less air so I think that may be why they both said that they suspected something was going on with the mass air flow is the only conclusion they can draw because something is making the mass air flow sensor either bring too much air in or not enough but I was just wondering could it be the wiring and what unplugging the mass airflow sensor means if it makes it run smooth

It definitely does, if I take it to a different mechanic or specialist what should I ask them to perform specifically, live data from MAF? Is there a specific place you would recommend having it serviced, Midas, Pep Boys?