98 1500 no first or OD trans

I have a 98 1500 it has 105,000 really clean truck. It was my mom's truck and since she passed away the truck doesn't get drove much,about 3 yrs now. The truck wont shift into overdrive and when you come to a complete stop it wont shift down to first, you have to manually down shift it. The engine light comes on it throws a code for 2 solenoids in the trans we have had it to 2 trans shops and both have replaced these solenoids and neither have fixed it. I have pulled all the connectors loose on the trans and they were all coroded i sprayed them with electrical contact cleaner and blew them out but wasn't very satisfied with the way they turned out. Still didn't fix anything. The weird thing is sometimes you can hop in the truck and it will work fine. One way we found to make it go into OD is shut the truck off while going down the road, wait until the speedo drops to zero, while still rolling down the road and refire the truck then it will shift into OD. I read somewhere on here about ignition switch causeing problems like this, what wires can i check on the trans to find if i have a low voltage problem.

Thanks for any help

This should be scanned on a trans function scanner which will show if the solenoids are functioning or not, as they can be commanded from the scanner, if a shop diagnosed this problem and replaced these solenoids it should be back in that shop for a recheck, no?

Both shops that it has been to have told us that they don't know what is wrong. They recommend changing the transmission, but they are in the business of selling transmissions. If the thing messed up all the time i would agree, but in warmer weather the truck will take spells of working flawlessly. I tired of spending money at the shop and not getting results, i am trying to work it from a different angle...if it was an easy fix i would like to think they could have fixed it.

Assuming they know what they are doing, I would expect some consideration on their part for the ineffective repairs. A bad connect6on anywhere in the harness from the ign. switch and the pcm and trans, can cause this as well as bad ign switch. All these issues should be checked especially when the condition is present, no other way here!