I am lost. Please please help

I drive a 99 chevy blazer with the 4.3 vortex in it. I bought the truck around this time last year and the issue has been there the whole time but is random and seems to get worse. I have racked my brains on what could be causing the issue but I have not found a resolution. Below is a list of the issues that I am experiencing. I am not sure if they are all one issue or multiple.
1. The check engine light stays on, I have had the codes read and it comes up for the gas cap, but I have replaced the cap three times now and it still stays on.
2. My abs light stays on
3. My truck has a shake with acceleration, I have had new tires, pitmans, idler arms, balljoints, suspension, checked mounts, replaced my transmission mount, had it realigned, replaced breaks and drums, the issue is still there.
4. Randomly the truck seems to sputter while in drive. It does it usually when the truck has set for say a day, but like I said it is random. I have thought that it was thirsty for fuel, but the gage doesn't spaz out. I have looked at my front end and also transmission and all seems right there, but when it sputters I still question them as being the issue. This issue has been there since I have bought it, but with it being random I never really worried about it. It seems to happen more ofter now.
5. Here lately, I have noticed that the service 4wd light is coming on after the sputtering happens.
6. The truck doesn't fire on the first turn over. Usually, takes two attempts before it turns all the way over.