BullyDog GT vs 545-RFE lost 3rd gear

Alright for starters I'll spit out what it is, what I've done, and if anyone with more knowledge on this subject chime in; 2005 5.7L, 4x4, 110,000km, I got a bulldog gt tuner from a kid saying "I lost 5th gear" and the tune was on an 09, I called bulldog got the proper tune for it, updates and all, took 10 mins. Plugged her in uploaded the tune, good. 2 days later a duramax flys by on the highway, instinct sets in, goose-er, trans kicks down, shoots up to 5000rpm, 110km an hour, and stops. At that speed, that rpm -no more acceleration with the petal held there for 4-5 seconds. Every once and awhile if mashed the petal, the trans would "bang" and jolt, then immediately down shift and merry on it's way, So I get it home and check the fluid, looks brown.. Yard it into work, throw it on the hoist and change out the filters, and fluid. Spin on included. Get it back together, start it up and it doesnt want to move in gear- level correct. P0700 code, (constant), Drive it 2 blocks with trans slipping, and open it up next day, pound the seal in on the push-in and try again; only has 1st and is slipping past that. Uninstalled the bully dog tune- Next day, new filter and gasket, new fluid, correctly installed (to get that 120psi seal) has 1st, 2nd -should be shift point -slip. Pulled the snap on scan tool out, monitored line pressure all good including in reverse 94psi, shifts 1-2-3 electronically good with scan tool, just not mechanical side. No codes present anymore.
Price on used trans with same mileage: $720.00
Price on brand new 545-RFE from local shop: $2400 my cost
Price on trans shop rebuild/fix "to be figured"

How do I prevent this from happening again?
Should the transmission be "built" with American made parts not Chinese;
Built for the tuner?
The near future I'm looking at a .276 duration cam, and headers, would now be a good time to build the trans to take abuse?

Yes now is a good time to beef the trans.
Also try a custom tune from a reputable tuner ( gonna need a diablosport)
I thought the bullydog tunes were pretty safe but it looks like either you original trans was on its way out anyway or these BD tunes arnt too trans friendly

If you are camming you are going to need a custom tune anyways so ditch the BD

Also just for info: WOT downshifts from overdrive are the number 1 trans killer, try to avoid.

Update

Since the trans has gone, I've priced out a few kits found one from a rather reputable site, 1200 and plus what ever shipping is, line pressure booster, shift kit, 1600 stall, and stronger clutches, I'm only going to want to do this once, I've never opened a trans before but I'm quite mechanically enclined, and if I need too buy specialty tools for the rebuild job I can, but the kit comes with a rebuild manual, should I try it myself? I'll have to find a diablo tuner for the cam, bd seemed good before this whole ordeal

I'd get an aftermarket converter if you gonna swap em out an get something in the 2600 range