It is a 1998 ML320 with 97k miles. The transmission fluid and filter were replaced at about 85k miles using the proper Mercedes transmission fluid.

The vehicle, just this morning, developed a slip in 4th gear only (a lot of revs but no power transfer (especially under load like when going uphill)). All other gears appear to be OK. When the revs are high and the tranny finally shifts to 5th, there is a bit of a lunge (jerky motion).

I did an OBDII check and there were no codes for the tranny.

The MAF senser was changed 10k miles ago and all is good there. The engine revs freely with out misfires.

Questions:
1. Could it be something simple (I hope) like a sticky valve?

2. If not simple, would a tranmission from an E320 4WD (210 Type, A.T., E320, AWD (722.664)) be compatible with the ML320?

Thanks in advance.