Just finished swapping out the 4.3/700r4 in my brother's '85 C10 for a 6.2/th400 out of an '88 R20 Sub. The Sub ran fine before we pulled everything, and it was running fine in the truck before we got the driveshaft in (was being lengthened). When we first backed it out of the driveway, we found a fuel leak and dropped the tank to check. We replaced the hoses and reinstalled the tank. Then on it's first test drive, it started out fine for the first few minutes, then began losing throttle response and stalled about 15 sec later. Now it doesn't want to restart. We've only been able to start it back up a few times, but it always stalls again after only a few seconds. It has new batteries (which we've been charging as needed) and 7 new Quickheats (one had swelled and wont come out). We bled the fuel filter and injectors several times, pulled the cover on the IP - full of fuel, and blew air through the fuel return line to see if it was blocked. We also jumped the glow plug controller with no luck. Is there anything we're missing/forgot to check?