First of all, check your fluid condition and level, wash the underneath of the truck, especially the transmission area. Check and clean all of your electrical connections on the transmission. Pay attention to your kickdown cable and return spring located on the driver side of the transmission, make sure the spring isn't bent and the lever moves freely. The check engine light could be something so pull those codes and let us know what you find. What I did for my truck was I made sure to grease all of the electrical connections and seal the top of the connectors as well as use hose clamps on any vent lines and run hose to the very top of the engine compartment. I haven't had any issues going through rivers.

 

Sounds like tranny is in limp mode. There are a number of excellent tranny threads in the DIY section.

Agree with everyone on checking fluid level (in neutral only) and condition. the vent on these trannys is located inside the TC housing - not a place you can do anything about sealing off. Dropping pan is not difficult. The typical mistake made is some have over tightened the pan bolts.

Go to the FAQ/DIY section and search for the thread on service manuals and pick the one for your year. The transmission section is very well written and can help you through the process. Do not use a cork gasket - get a rubber one. And +1 on the drain plug. Dodge did not install them on these, but it will save you time later on. And only use ATF+4 fluid - with no "majic" additives or other snake oil. And do not let anyone "flush" your transmission. It will only make it worse!

Post up the code when you get it read. It will help also.