What would cause this???????

1993 GMC 4/4 4.3L with a 5 speed, I need some help on this one guys.
The truck has 220,000 miles on it, I just bought it 4 weeks ago and it's acting real strange.

What it's doing is when i go down the road in 5th gear the truck will just lose power like i turned the key off, then i will down shift into 4th gear and put it to the floor and it will take off again. It seems to do it when i get about 2 or 3 miles down the road at 55 to 60 mph.

This is what i've done so far.

Replaced the motor with a new GMGoodwrench reman because the other one was starting to knock and i didn't want to blow it up. Like i said i just bought the trk but i did notice with the other motor it also had a dead spot init about half throttle, so i'm thinking that it must have something to do with the electronics..???

I've changed the o2 sensor because the scan tool showed that the ecm wouldn't stay in closed loop, it was going from open to closed. After i replaced the o2 it now stays in closed loop. The only code i've got was CODE 42, Ignition Control Circuit. But i don't know if this would cause this type of problem???

I've set the timming to TDC at 0 Deg. with the advance wire unpluged.
New spark plugs, I have a new knock sensor but i haven't put it in yet because i'm not sure if that would be the problem.
New fuel pump and filter. New exhaust but the trk don't have a Cat. it was removed before i bought it. I've unhooked the EGR valve vac line. and tried it but the trk still wants to die out only when i'm going down the road, the trk will idle when i stop.

Thanks for your help. Dave

You might want to check your tps sensor, possibly has a dead spot in it.

Since you have an ignition control circuit code I would also check for play in the distributor, with 220k Miles on it it may have alot of play in the bushings. My friends 93 Suburban was kicking out that code and a new distributor fixed it, had alot of play in the distributor shaft. (easily checked, remove distributor cap and rotor and then see if you can wiggle the shaft from side to side, if it moves then your bushings are worn out)

You might want to check your tps sensor, possibly has a dead spot in it.

That's what I was thinking. Can you throttle past the lack of power?

Thanks for the tips guys,
I'll check the tps and the distributor shaft out tomarrow.
I really think it has some thing to do with the distributor or timming just because of the miles and the code that came up, but the tps is also a good one to check.
I think the guy that i bought the trk from already replaced the cap and rotor and wires because they look fairly new.
I think whats real ood is that, a few days before this started to act up this bad I drove the trk like 100 miles and it seem to run ok. But after i put the new exhast on it then it acted like it wants to die out???
I do alot of wrenching but this one really has me going...Hmm.... Thank again and i will post what i find wrong. Keep the tips coming.

i think the problem might be the ignition module. but i guess a new distributor has a new module so replacing the whole thing would fix it

Well it's fixed. Thanks for all the help.
I pulled the dis cap off and the little pin that comes down from the coil was whore out. Boy do i feel dumb....
When i put the motor in i checked the cap out good madder in fact i even cleaned the contacts where the wires plug in and it all looked ok, So the last thing i would of thought was the dis. cap.
I replaced the cap and rotor. All fixed up.....
Thanks again. Dave