acceleration problems

We just purchased a 98 Dakota and it is having an acceleration problem.  It does it only sporadically.  when our mechanic hooked it up, he found that someone had disconnected some wires under the dash so the check engine lights didn't trigger.  He replaced the manifold gasket and cleaned up some animal nests that were in there but it still won't accelerate properly.  Now we also are having trouble keeping it started.  The mechanic put a fuel pressure gauge on and the pressure is fine even when it acts up.  He replaced a coil and something else but it is still doing it.   I don't want to keep replacing parts on it if we cannot find what is wrong with it.  Would I be better off bringing it to a Dodge dealer and having them fix it or at least tell me what is wrong with it?  I thoroughly trust my current mechanic.  Thanks