i got a 99 dakota with a 3.9 and every once in a while it will seem to lose fire or something like that ,it will spit and sputter as long as its in gear,put it in nuetral or park and rev it up a little and it works fine.but when you put it back in gear it will do it again and eventuallyit will come out of it.now it is like it slips out of gear or something your going the same speed ,tranny not slipping or nothing and rpm guage fluxuating rapidly sometimes going from 1500 rpm to 5000.any help would be appreciated,dont know where to start.
thanks guys

 

Check simple things spark plugs rotor and cap, plug wires

 

tryed and replaced them all