I just bought this 88 10th anniversary T2 for $400 and it runs great untill about the top of second. At like 6200 the car starts miss firing it seems like and stops pulling then when i put it in third its fine untill about 6200 then it starts doing it again. The car is bone stock but someone took off the exhaust after the cats and has brand new plugs and wires. Does anyone know what could be causing this?

 

i would check in this order
plugs
wires
coils