Have a chance to buy a super nice '94 with 5.8 and E40 trans. He says that occasionally when it goes from 2nd to third it feels like it goes in neutral, if he backs off on the gas and speeds up again it works fine. Does this sound like a major problem?

 

Almost any problem with an E4OD is a major problem. I would test drive it to at least 2 shops for an inspection. Then start your bidding. Good luck.