Some observations, comments, . . .
When the car is being driven, and the accelerator pedal is pressed down, engine torque is increased, and there should be a corresponding acceleration of the car. If the engine revs up, without any corresponding acceleration, there is some sort of "disconnect" between the engine output and the wheels. This could be in the engine/torque converter connection, the torque converter, the transmission gear set, or the drive train to the front or rear wheels (drive shafts, differentials, axles). The converter and transmission are less likely if two transmissions with their own torque converters were installed properly and the car is exhibiting identical symptoms. All the more so if the car had the exact same symptoms when first purchased, before changing the tranny. That essentially leaves the drive trains to the front and rear wheels.
There have been cases of a CV joint in an axle failing, but not falling apart. Visually it looks fine. Moreover, if one twists the two ends of the axle by hand, it might seem intact because of residual friction in the joint. But when that twisting involves higher torque, the joint begins to slip, and torque transfer is lost. The part that is connected to the differential spins freely, and that reduces the torque available to other wheels. The engine revs but the car doesn't accelerate. Similar symptoms could be experienced if an axle has pulled out of the differential. A movement of about 1/4" is enough to disengage the splines on the axle from the splines in the differential side gear. The axle appears to be in place (not hanging down), but it's not connected inside. I'm not saying these are your problem, but the symptoms would be similar to what you experienced, especially most recently when you "gave it some good gas on our gravel driveway. . . "
All four? When in Park, the front wheels should not be turning. The parking pawl in the tail section engages a gear tand pinion shaft connected to the front differential. The pawl prevents the gear from turning, and therefore the front drive from turning. Are you sure this was in Park?
Very little torque is required to turn the wheels when they're raised. This doesn't simulate the conditions when the car is on the ground and a lot more torque is needed to move the car.
To be expected. When the pedal is pressed with the car raised, one wheel could stop while the others continue to turn. To the ABS, that's a skidding wheel and so the ABS kicks in to control the "skid".
When the car is being driven, and the accelerator pedal is pressed down, engine torque is increased, and there should be a corresponding acceleration of the car. If the engine revs up, without any corresponding acceleration, there is some sort of "disconnect" between the engine output and the wheels. This could be in the engine/torque converter connection, the torque converter, the transmission gear set, or the drive train to the front or rear wheels (drive shafts, differentials, axles). The converter and transmission are less likely if two transmissions with their own torque converters were installed properly and the car is exhibiting identical symptoms. All the more so if the car had the exact same symptoms when first purchased, before changing the tranny. That essentially leaves the drive trains to the front and rear wheels.
There have been cases of a CV joint in an axle failing, but not falling apart. Visually it looks fine. Moreover, if one twists the two ends of the axle by hand, it might seem intact because of residual friction in the joint. But when that twisting involves higher torque, the joint begins to slip, and torque transfer is lost. The part that is connected to the differential spins freely, and that reduces the torque available to other wheels. The engine revs but the car doesn't accelerate. Similar symptoms could be experienced if an axle has pulled out of the differential. A movement of about 1/4" is enough to disengage the splines on the axle from the splines in the differential side gear. The axle appears to be in place (not hanging down), but it's not connected inside. I'm not saying these are your problem, but the symptoms would be similar to what you experienced, especially most recently when you "gave it some good gas on our gravel driveway. . . "
