@Clint 80series I assume you have an A442F transmission.
The solenoids aren't likely to be the problem if the problem goes away once the transmission oil is warm; same for the control cable. These are the usual root causes of poor A442F performance, but the problems are persistent, and not typically transient and only present when the oil is cold.
You don't need to replace the valve body, even if the spool valves or their bores are worn, but you can't be certain that it's not leaking internally unless you vacuum test it. A good transmission shop can do this, but you may not have one on the island. At any rate, I doubt that's the problem. I say this because the oil thins out, just a little, when it gets warm and if the spool valves were leaking, the performance of the gearbox would be worse when the fluid is warm, not better.
I have one question before I offer a possible suggestion for resolving this problem: when you put the truck in reverse, whether the oil is warm or not, and back up quickly, does the transmission slip out of and back into gear? You would notice it immediately if this were the case; the shock of going back into gear is jarring. By quickly, I mean faster than you could easily walk, and it takes a couple of meters to see this happen.
LMK and I'll try to give you more advice.
