"any reputable shop would 1) NEVER use the incorrect socket size, 2) NEVER use an impact gun to tighten a fill (or drain) plug, and 3) would immediately replace the plug with a new one."
1) Neither would I, 2) Definitely not, 3) Absolutely.
I went with 3.25 quarts MT90. I'll be ordering a new plug before too long (do your low-pro plugs work here?) and welding a piece of flat stock with a hole in it to the head of the plug and getting it loose. There aren't any leaks that I can see. Probably just someone being lazy and with only 3/16" of plug head and a socket with a chamfered inner edge...
I'm still amazed at what I find both shade tree mechanics AND "reputable shops" getting away with. I changed the plugs on this one when I went through the rest of it and was pleased to find that they were the stock NGK's. Then I got to the #3 plug and found cross threaded and only (thankfully) 1/4" into the threads. The back-tap worked great for this and only set me back $40 and a week for shipping. When I triumphantly finished that task I pulled the #5. It was an Autolite that was who knows how old. Other than this I found red RTV in palces it didn't belong, a pulley installed backwards (seriously, the PS belt was 1/4" out of whack), and a missing bolt or two. I don't know how the thing made it the 6 hour drive from where I got it (in partial trade for a little work, thankfully) but my hat's off to Toyota. I didn't get the Yota thing before, but now I do.
A new timing belt, water pump, tensioner/pulley, idler pulley, fan bracket, cam seals, crank seal, rotor cap/button, wires, fan, condenser fan, shocks, springs, fluids, rear wheel bearings/seals/shoes, O2 sensor, cat back exhaust, fuel filter, and MC shifter bushing later...whew, and this thing runs like a champ. All stock parts other than the es3000's and moog rear rear springs/dayco 1 1/4" spacers. A set of 31/10.50 mudders and a fresh alignment topped it all off, and I couldn't be happier. My late model 2500HD 4x4 hasn't moved since I got this thing going. I'm hooked on it for the foreseeable future and I thank you guys for providing a forum with so much info and a company with such great CS. I ordered two of your rear axle service kits after getting my shifter bushing/boots, and when one came with the wrong seal (non abs type) I had the right one within 48 hrs, no questions asked.
I took my wife out for some light wheeling and she had a blast. I call it my "ATV w/AC". Despite being mechanically neglected, every bell and whistle on this thing works, the compression checks out, and leakdown test was all good. I'll be in touch when I get ready to take it to the next level!!