rough idle

so here is the deal, i have a 1989 GMC k1500, 350 tbi... recently i started having problems with the fuel pump cutting in and out, so i checked the wiring and such, and turns out there must have been a loose connection somewhere because just moving the wires around fixed the problem temporarily. it happened a few more times then finally for good. i towed it over to my dad's friends' house and he replaced the ECU, now it starts right up every time, but runs rough at idle, after idling for a minute it cleans up and runs fine, then drives fine after that. also it seems to idle worse after its warm. i read that the truck needs to be driven in order for the computer to learn the air/fuel mix and what not, but im coming up on 100 miles since the fix and still no changes. any ideas?

so here is the deal, i have a 1989 GMC k1500, 350 tbi... recently i started having problems with the fuel pump cutting in and out, so i checked the wiring and such, and turns out there must have been a loose connection somewhere because just moving the wires around fixed the problem temporarily. it happened a few more times then finally for good. i towed it over to my dad's friends' house and he replaced the ECU, now it starts right up every time, but runs rough at idle, after idling for a minute it cleans up and runs fine, then drives fine after that. also it seems to idle worse after its warm. i read that the truck needs to be driven in order for the computer to learn the air/fuel mix and what not, but im coming up on 100 miles since the fix and still no changes. any ideas?

1. for 89, you don't have that smart ECM. but it takes very little driving time to learn proper driving cycle.
2. you can still read error codes, which i'd have done
3. folow this:
http://www.2carpros.com/first_things/why_does_my_engine_run_rough.htm

so here is the deal, i have a 1989 GMC k1500, 350 tbi... recently i started having problems with the fuel pump cutting in and out, so i checked the wiring and such, and turns out there must have been a loose connection somewhere because just moving the wires around fixed the problem temporarily. it happened a few more times then finally for good. i towed it over to my dad's friends' house and he replaced the ECU, now it starts right up every time, but runs rough at idle, after idling for a minute it cleans up and runs fine, then drives fine after that. also it seems to idle worse after its warm. i read that the truck needs to be driven in order for the computer to learn the air/fuel mix and what not, but im coming up on 100 miles since the fix and still no changes. any ideas?

because this is a rust belt vehicle and very old check all grounds for security and no rust...at ground junctions.....