Weren't the earlier units filled with BOT 402 GL4 75w85..... GM moved to 303 for better MPG or maybe because of limpwristed snowflake complaints. Little hint.... shouldn't be adjusting fluid viscosity for shift quality. Install a temperature sender/gauge would give you better R&D then the marketing/accounting engineers at the automaker. Does GM still sell either 402 or 303?
I don't see the bearing failure as an Amsoil issue. Upgrading from a 70w or 75w to synchromesh fluid, even though not stated GL4, but still has excellent additive package, wasn't the cause....
I doubt it was a fluid problem. GM bean counters at work!
My ol' 7.3 powerstroke is a guzzler..... should I dump the 15w40 for a 0w8 oil and drain the differentials from 75w140 to a 75w80? This is pretty much what went on with manual transmissions at all automakers.
I would say that GM did some interesting case design work to move fluid around for better temperature control within a running transmission(seems that most automakers copied it), kinda like what GaleBanks did with their 'differential cover' comparison. Obviously, it wasn't enough for all transmissions. Seen a rash of various failures among all makes that didn't make sense, other than common move to thinner fluid.
Use the OE or the Redline LV fluid. It will give you the best MPG. The future failures are inevitable. If it were mine, I'd use the BOT402 or Redline MT85 and thumb my noses at the MPG. And when cold, just be patient with the transmission. All manuals can be a little annoying with cold. Its the nature of the beast. The SAE140, pretty sure solid like a bar of soap, used in a company fleet was a little difficult to shift 30 years ago, especially in winter.... nothing like battling with reverse, and then riding 1st gear thru the company lot, and out on the road 1/2 mile before 'attempting' a shift to 2nd. Manual transmission are nothing like arcade/video games with their pseudo shifter.
A good transmission shop can swap in a Sega Arcade shifter into your vehicle... and you can have all your shifting fun in the driveway. Too many learned to drive a manual in a video game.