Fluid is very dirty was changed recently tranny slipps when you take off vibrates should change fillter and tranny oil again or is tranny going out,

The Vacuum Modulator sounds like a good place to start. I would
change the Transmission filter and gasket along with the Transmission oil. Dirty Transmission fluid with a dirty filter can clog
the valve body and cause this.

I always run a quart of tranny fluid for a week or so old and change the oil tranny fluid helps to clean the oil system out

according to my alldata book this vehicle doesnt need the tranny oil changed ,if it fails then its a exchange gearbox ,if you have a dipstick for the tranny then just undo the tranny sump bolts and drain it this way but my honest advice is if it works well leave well alone as the oil shouldnt get dirty or deteroriate as its only a hydraulic pumping oil but if its dirty then the bands and the clutch are worn so it will require a overhaul anyway as it will give up the ghost before long

well first check you transmission fluid if its low add fluid. and check undercar for small spots of fluid. transmission fluid is red in color. if its not a fluid problem try and remember if you are on a up grade or down grade the next time this happens. and yes when your transmission slipps you RMP will naturaly rise because the motor is not engauged with the tranny. and if your fluid is fine you may need to have a diagnostic test run to see if you have a sensor going bad on it. and if the fluid is low but you have no spots of fluid in driveway. it may not be leaking just low the car is over 10 yrs old and may have just used a little fluid over a few years. i hope this helps...

It sounds like you either have a dirty filter, or a solenoid is faulty in the transmission. Change the fluid and filter, put some Lucas transmission oil in it and see if that resolves the issue. If the solenoid is dirty then it will cause the transmission to shift improperly, the Lucas will clean it.

If you have a vacuum modulator on the trans,it could have a bad diaphram and **** trans fluid into the engine.
Now I do not know what model or unit trans you have. No vacuum mod,then the dealer is correct.
You can look just above the trans oil pan, near the rear, for that part and easily change yourself. Get at auto parts store. It will be the thing with a 3/16 vacuum hose on it,going to a port or vacuum switch on intake manifold

did you have your alingment checked out?

well to start of if you buy it you will need to get the tranny fix and if it is front wheel drive you are lokkibg a spending a good chunk of change.also tell the person who is selling the car to have the tranny fluid changed out make sure you see the fluid change out on the tranny that could be the proble the tranny fluid can be dirty.remeber go with him when he has it change.and also make sure the filter is changed out to .hope this helps out let me know

try checking the fluid level in the gearbox,rodeo dont have a dipstick so u have to undo the plug on the side of the gearbox just like a manual gearbox.if the oil is really low i suggest doing a full service on the gearbox,change the oil and filter is ideal for better results.