Astro Idle Problem / Slower acceleration

I hope someone can give some advice as to what to try next. I have a 1988, 6 Cyl. 4.3 Astro van, awhile back I did a full tune up (rotor, dist. cap, plug wires, air filter, plugs, fuel filter, oil filter, oil change), the van ran fine for a few weeks and then I noticed that during complete stops the idle became rougher and rougher it got pretty bad and it worsened over the weeks and got bad enough as to where I didn't want to take the vehicle on the road to avoid getting stuck. This past week I took it to the shop where they had installed a rebuilt engine in the van about 2 years ago. The mechanic there ran a diagnostic on the van and said he noticed one injector was malfunctioning, the spraypattern was off and it had a small steady fuel stream from the center of the injector pouring right into the butterfly valve (I hope that's the right description), anyways I guess I'm like alot of people that want to try to keep costs down and do it yourself helps alot. The part number on the original injector that's defective is GM5235134*RPD, at the other side of it there is an additional number 9167 GM. I contacted the local Autozone and took the part with me to compare, they entered the number and said it was a Borg Warner part, unfamiliar to me but they suggested the equivalent would be a GP Sorensen 800-1801N. I noticed immediately that the injector tip was different, the original has a small tiny opening at the end, as to where the suggested replacement has about 5 small openings, they seem recessed and it seems to have a small cone pattern inside the tip going towards the openings. I replaced the defective injector, gaskets, checked for leaks and fired the van up, it still showed a rough idle but I then noticed what seemed like small misfires inbetween the idling. The thought was since the engine had run bad that the plugs might be fouled so I went today and got new plugs and replaced them, the old ones are extremely dirty and black. After this the van had a pretty good and smoother idle. The problem I noticed was during a test drive that when I took it onto a main road and went to accelerate that the pickup during acceleration has noticibly decreased, so I'm wondering what to check next. I know that even when the bad injector was still in place that my van would have extremely good pickup and go. I would be grateful for any suggestions to help me get my car running good again.
- Don