Ok, I'm new to this forum and have done quite a bit of researching online but only a few answers have popped up and I have a couple questions. I recently picked up a 2005 Endeavor 2wd with about 130k miles. It drove fine for the 1st 100 miles or so to get it home and to and from the airport once but on my way back home from work on the Interstate, upon decel off the ramp there was a clunk/jerk like it slammed a gear type sensation and then got the blinking neutral/transmission limp mode situation. Codes I got from my generic reader were initially a PO734 and then after trying to move back and forward at home later on a PO736 came up. Just for some background, the fluid looks OK in color and does not smell burnt and I cannot see anything obvious on the stick. The level appears ok too as long as it is checked on level ground in neutral...I don't have manual on whether it should be neutral or park to check. Also, no leaks or obvious wiring damage that I can see but I will look more tomorrow when I have time and daylight again. It was raining all day today.

My question I guess is what causes the somewhat sudden situation? I've read about the wave ring breaking but that seems to create a more undriveable situation rather than a limp mode (stays in 3rd gear, need to rev up to like 2k rpms then it lurches forward...very abrupt to get it rolling) and the other is debris in the transmission from like the nut backing off internally creating metal shavings from planetary contact causing essentially fluid flow/pressure issues throwing it into limp mode. It drove somewhat fine prior and then this suddenly happened. However I have only owned it a very short while so there could have been previous signs I was not aware of prior. Long story short, what could this likely be and is there pretty much only way to fix going to be replace the transmission? I just want to make sure there's nothing like software or external issue that can cause this too before I condemn the transmission on a car I just got and have not had any prior time to become familiar with enough. Thanks everyone.