I have a 94 grand cherokee with a 4,0l that surges and bucks, will sometimes stall at a light. in park, will idle high and then low, keeps doing this, have replace the throttle positioning sensor but no change

Most low idle speed problems on these engines are due to a faulty idle air control valve but since you state the idle will go up and return to idle then i would say it is working properly i think you have a throttle body coking problem ( dirt and grit accumulates around the butterfly valve in the throttlebody ) to fix this simply remove the fresh air hose from the throttlebody and open the throttle all the way up use a clen rag and wipe clean you may use a solvent such as B12 on the rag but dont use too much

check throttle position sensor

Check your Idle Air Control Valve (IACV)

try this procedure it will help wit the idle, don't know about the overdrive issue.
Here is the most common cause of surges and stalls at stops and low erratic idle speed and rough idle, it is the idle speed control air-bypass valve and throttle valve (IAC for short), they get full of gunk over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

put a throttle position sensor on the throttle boby this should fix the problem!

Mine does the same thing when the oxygen senor goes out... About every 70k miles. doesn't always turn on check engine light

Here is the most common cause of surges and stalls and low idle, it is the idle speed control air-bypass valve and throttle valve (IAC for short), they get full of gunk over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

TRY THIS PROCEDURE:
Here is the most common cause of surges and stalls and low idle, it is the idle speed control air-bypass valve and throttle valve, they get full of gunk over the miles and cause idle issues (stalls) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake

check your transmission fluid,the motor will stall when fluid is low

A faulty gas cap can cause the sensor to come on.
Clean out the throttle body with a cleaner and see if the idle improves.