Ok so its been a minute since I've had a chance to get on here! Here's the update.
1. Ive been driving it in Tow/Haul since I posted this thread. TH mode seems to make it a little bit better, but not all the way. I would say that TH has 10-20% the shudder that normal driving has. Again mainly in 5th - that being said, either Im paying more attention, or the symptoms are spreading, as outside of TH mode it seems to be in 3-5 now. Less in the other gears, but still present.
2. I got the truck at 143k - and the only service history I can confirm is a water pump about 10k prior to that.
@Dusty As far as plugs go, I have no idea.
@Marshall same goes for fluid and filter change. Plugs have been on my list, just havent had the time recently. For that matter.... a trans fluid change and thermostat mod have also been on the list too...
3. No codes of any kind have been thrown recently. As a matter of fact, the only codes Ive ever gotten are codes for fuel tank voltage out of range (over a year and a half ago that went away on its own), and a code for my 3 way coolant valve. The valve body is still there and plugged in to avoid throwing a code (most of the time), but the actual coolant lines are hooked up to a 3 way pipe fitting and always open.
So. I did go to the store yesterday and got two tubes of shudder fixx - transmission was too hot today after dropping the kids off at school to put it in though... so that'll have to wait for the weekend.
Any thoughts/suggestions as to some next steps? Shudder fixx right away? Would a drain/fill be beneficial? I think I saw on some other thread something about a flush product designed to clean off the glaze that
@BenWade was mentioning. Any ideas?