On my 93 Nissan quest, during acceleration the van has a slight hesitation. She'd had a full tune up (plugs, wires, cap, rotor, fuel/air filters, pcv valve), as well as the timing belt/water pump changed. The hesitation almost seems to occur during shift points. Mostly noticeable around 40 MPH. What type of other things should I start looking at? The transmission fluid level it good, I checked that.