The engine is a 4.9 ltr 300 cu in inline 6. One of fords best engines. It sat for a little while so I decided to get the old thing up and running so it wont become a permenant yard ornimant. the first thing I had the shop do was rebuild the the clutch master cylinder and replace the brake master cylinder and make a few minor wire repairs and such to get it out of its slump. So I took it to a reputable shop and they did the repairs and had no problem. I drove it for awhile and it didnt get very good fuel mileage(which I didnt think much of for it being an old truck) but i figured that it was time for a good tune up. Since this is my grandfathers truck there was no telling when the last tune up was. So I take it to them and tell them I want plugs, wires, cap, rotor, fuel filter, air filter, and finally a nice oil change to top it all off. They gladly accepted the job and asked if there was any running issues or was just wanting a tune up. I told them that the fuel mileage was a little poor and it was time to get a tune up anyway. And what I mean by poor fuel economy I mean like nothing more than 10 mpg. I really didnt think it was going to get much better than that to begin with. So they did the work and when I got the truck back I noticed something wasnt right. For one, the damn thing was missing and second, the cruise didnt work. So i took it back up to them and told them what was going on and they said they would look at it. When i finally picked it up they still couldnt find out why it was missing or why the cruise wasnt working. During that time they found out that the distributor was way out of wack so they timed it. They did do a compression test on it and all the cylinders tested from 145 psi to 155 psi. They are saying that it could be caused from excess carbon build up on one of exhaust valves causing it not to seat all the way. But the biggest question is wouldnt that cause it to have low compression? And if it is indeed carbon buildup is there anyway i can fix this problem without taking the head off. I can do pretty much anything to the truck. I just need to find the time to do it. PLEASE HELP!!! Thank you!