CAT plugged?
Exhaust bent in a way, or folded by someone trying to bend it in some way?

 

 

So strange.
Try taking off the battery for a bit, so the computer "relearns".

Mine did this once - brought it to a shop in 93 and they rebuilt the bottom end. I really doubt that was the problem, because your problem sounds just like it - seems exhaust related. It drove, but zero power. Give it gas and it makes a deeper sound but doens't move. Feels like 20hp.

Really interested in what others with say here.

 

Does the check engine light do anything?
Try to read the codes from it. No obd.

Oxygen sensor is installed and hooked up?

 

 

It would be helpful if you mentioned exactly what muffler was put on it.

 

 

Packaging material crammed in muffler? Can you see through the muffler with a flashlight? Can you have someone blast compressed air in before the muffler while you feel for air flow at the exhaust tip? Welder used a flange that was significantly smaller diameter? How did you go about deleting the EGR?