Toyota A750E Transmission

I have a 2006 Toyota Tundra 4.7L V8, 2WD, with the A750E 5-speed transmission. Due to a company car for 8 years and recent remote work, it only has 200k miles. I have driven this truck for 20 years and maintain it meticulously. I know every creak and rattle, it is literally an extension of me. I have done all the maintenance myself (front end suspension, driveshaft, timing, water pumps, radiator, etc.) minus the new steering rack. It's been fantastic.

The last several years the transmission has a firm shift from 4th to 5th in the winter temps when under light acceleration. This is even if I let it warm up for 5 min or so after a cold soak in the low teens (10-18deg F). When I accelerate with a moderate or heavy foot, it shifts mostly fine. It's typically ONLY that first cold shift and ONLY from 4th to 5th. It doesn't slam into gear, but it's noticeably more firm. I typically do a transmission drain and refill once a year. Most recently, I did it about 8 months ago. The pan and filter always look pristine.

Should I not over think this, or is it worth cleaning a solenoid or two? I've never messed with a solenoid or valve body, but it seems well within my mechanical comfort range. Two years ago I did my valve covers and those cam shafts look excellent. I want to keep this thing for several more year yet.