No second gear on automatic upshift

Finally got the whole rig back together, been driving a couple of days. Took a longer drive, about 80 miles and on the way it started missing second gear on upshifting. Not throwing any codes, just shifts from first to third then on up. I can manually down shift from 4 to 3 and then on down to 2 and when slow enough to 1. Tranny only has about 7k miles on it since major rebuild by super reputable mechanic, has worked really nice, solid, firm, quick upshifts every time and not violent either. No hotrodding, seriously. Have been told to check the solenoids but the ATSG manual for this transmission says all failures for missing second gear are mechanical, but second gear is still there so it must be electronic? Right? What advice do you folk have to offer?

With that low of mileage since rebuild, I would talk to the rebuilder.

I would, and have talked to him but the truck sat apart for 7 years and that has caused him to feel less than responsible, and I am sure it is an electronic failure, not a physical failure. I'm still looking for a cure. The funny thing is that in the event of total electronic failure it is second gear that it defaults to, not skips. Thanks.

Maybe there are no codes but how about double check the wiring.That multipin connector on the trans and even the connectors on the puter might need a close look.

Sitting for 7 years? That's not great for it either.

Have you pulled the pan? Changed the filter? Gotten rid of the fluid that is probably not quite up to spec anymore?

I would be tempted to pull the solenoids and ensure they aren't plugged.

Have pulled and checked, multiple times, the plugs on the transmission. Took it back to the mechanic that rebuilt it and went for a drive, did some testing and he says the shifts are delayed and hard, sounds like a TPS problem to him.

Hooked up GMTDScan Tech and discovered that it shows no vehicle speed though my speedometer works just fine. Going to check out the VSS more closely when the rain quits, also will remove and clean the TPS.

I'll let you know what I find.