350 tbi will not idle or drive

I was given the vehicle listed above with a 350 tbi. 2500 with service bed and finally got it home. It had sat for about six or eight years. I put a battery in it, new fuel pump and filter and primed the throttle body and it started right up, it idled well considering the circumstances. I was able to drive it across the subdivision and back, about four miles with no problem. And again the next day just a block and back. On the second, short trip it began to be difficult to keep running when in gear. (It is A/T by the way) gradually but quickly it got worse. Now it would not run unless I was constantly and gently pumping the throttle. I have cleaned the throttle body, tested the IAC and TPS with a multi-meter, adjusted ignition timing, and looked for vacuum leaks with starting fluid. After the timing adjustment I was able to get it to idle but it was mildly to moderately rough. I thought I was on my way but when I put it in gear it begins to sputter and backfire. I cannot even get it thirty feet before it shuts off. It does not jump forward forcefully or jerk it just idles down and then spits and shutters till it dies. It will start right back up but usually afterwards it usually will not idle. It seems there is little difference in the engine temp. I would like to get some some ideas for troubleshooting, but I have very basic tools and no access to most tools needed for testing (i.E. Vacuum pump, pressure guages, etc.) Any and all useful information will be greatly appreciated.