I've had my US Gear Overdrive in my truck for over a year now. It's had a temp sender in it since the day I installed it (I did it myself, it's NOT DIFFICULT AT ALL), and the temps have never gone over 220-230.
Heck, my average temperature on the OD when towing is in the 150-180 range. It only gets over 200 when I have a full load (GCWR of about 18k) pulling a hill that's more than just a couple miles long. It's full of one quart of Redline 75W-90 gear oil, and I changed it once about 6 mos ago when I had to replace a defective SPA temp sender (the sender is mounted in the drain hole).
Installation... anybody charging $1000 to install it is seriously ripping you off. I'd gladly do it for $500 but I'd still feel like I was ripping you off. You and a helper can do it in an afternoon. The helper's only required if you can't benchpress 150 lbs easily (the xfer case weighs 75 lbs and the OD is 65 lbs)... it's just easier to have help when sliding the stuff into place.
Heck, it took me longer to run all the wires into the truck and up the shifter than it did to install the overdrive itself!!! And I'm a scrawny little f--- too (5'8 / 140 lbs).
Rob