my 98 ram 5.2 4x4 was fine up until now this morning worked fine on my way home it started shifting into overdrive hard and after awhile i heard some gears grinding so i pulled over and checked fluid... fluid level fine and fluid dident look bad.. kept drvign. overdrive getting progressivly workse until the trans temp light came on pulled over waited to cool and got it home.. check the trans cooler and doesnt see even the slightest bit warm.. i dont even know where to start...any Ideas?

 

Do the check valve delete that you'll find in the FAQ/DIY section. Flush the cooler, then replace the transmission filter and do a full ATF replacement -- not just draining what's in the pan, but going for the whole enchilada.

http://www.youtube.com/watch?v=MsdPAadc9fY

Ignore the bit about using Dexron-III.

 

I would check the check valve going to the cooler... they are notorious for plugging..there threads here on removing them altogether...