When driving through my gears the engine seems to dip and peek and slow to build up a speed, the engine ticks over fine when in neutral. Driving in gear the vehicle is slow to build up a speed, the engine some times races and then dips, always driven without flooring the gas pedal. The engine ticks over fine without racing or stalling when in neutral. Its a diesel ford transit connect.
It slounds like the clutch packs or the torque converter is bad. It might be because a solenoid that actuates the clutches for different gers failed, but if it is slipping, you probably need a rebuild.
Take the car to a transmission shop as automtic transmission require specific knowledge and special tools. Repair shops will just send the transmission to a tranny shop any way and you will pay more maoney and you won't have contact with the transmission rebiulder.
AAMCO is overpriced and you can find a reputable tranmission shop near you by using the search engine on this site.