Toyota Repair: 4Runner transmission, exchange unit, transmission overhaul

Question
I have a 94 4Runner, v6, automatic transmission, 4 wheel drive with 171000 miles on it. The transmission sometimes slips in drive when starting from a dead stop. Car will not move but tach revs up. When I pull the car down into gear "2" it will then move forward. Once moving I can shift back to "drive".
Will this repair involve a transmission overhaul or is it something simpler?

Answer
This is an indication of an internal clutch piston leak,probably the foreward clutch but in any case the transmission has a serious problem, I would not recommend an overhaul because in the end it may cost a lot more than just getting a remanufactured exchange unit, this way you know up front what it will cost, a transmission shop may quote a price going in but after they open it up will find other parts it may need which could be very expensive, the price difference between a used transmission and a rebuilt one will be minimal, usually between $1,800-$2000 for the transmission plus labor time to install it.  Considering the age and mileage you may also consider trading it in on a newer model.