So just the other day I was out doing a bit of casual offroading. Noting crazy, just crawling through some washes and climbing some small, easy hills in the local AZ desert. As I came through a spot of fairly soft sand, my truck started to feel as though it were getting stuck/buried in the sand. The tach read 3000 RPMs, but I was going nowhere. I knew better because I have never had any trouble getting through sand, no matter how deep. The feeling I felt was the transmission slipping/binding. I had the tranny in D2, so I came to a stop and shifted back up to D and drove right out. When I got to a flat, solid surface, I decided to check the transmission fluid. I thought maybe it was a bit low because I have a very small leak at the shifter linkage. So with the truck running and up to temp, I removed the fill/check plug and about a quarter to a half quart came spewing out! It finally settled down to a dribble and I ran it through the gears. I thought maybe it was low, but maybe it was actually over-filled from the last time I put tranny fluid in it??? Any input here? I may have gotten overzealous last time I filled it and put a bit too much in. However, I am noticing that the shift points have changed, it is shifting at a higher RPM than before, almost like it's in power mode (but it's not). I also noticed that the fluid is really dirty. Wondering if I should drain and fill it?? Thanks ahead of time for any input or advice.