Possibly a vacuum problem or transmission solenoid. This will have to be properly diagnosed in order to definitively determine the cause.
Bad transmission rebuilder
I don't think so. The automatic transmission is controlled by engine speed, vehicle speed and throttle position. A large vacuum leak could effect throttle position, but it would cause other problems more noticable than the effect on transmission shifting. a vacuum leak mpuld not cause trasmission to slip but a band inside transmission would cause the problem
ABS has nothing to do with the transmission engaging on this vehicle.
If the transmission is healthy and any/all adjustments are done properly there should be no slippage.
Try checking the vacuum lines on the axle.
Sensors got wet
Yes - could cause fluid to foam and not lubricate properly
One thing that can cause this is a slipping automatic transmission. The clutches do not engage at first letting the engine run free, then they engage suddenly producing a slam or jerk. This will quickly destroy a transmission.
On cars with an electronically controlled transmission, the answer is yes. The transmission may not shift properly.
There are several things that can cause your engine to misfire and the tachometer to not work properly. The most common cause is a malfunctioning vacuum hose.
on some cars there is a automatic transmission modulator valve that tell by vacuum when to shift gears. If that valve goes bad you will get tranny fluid in your lines.