1993 6.5 CK3500 1 ton Trans problems
 

1993 6.5 CK 3500 automatic transmission won't run in drive or reverse most of the time.
I changed the fluid and filter and there was small metal pieces in the pan. I put a bottle of Lucas Trans fix and drove the truck in drive for pulling a trailer for 200 miles and then when I went to regular drive on the highway the truck drove fine until I got off the highway and was going 35 mph and lost drive and reverse. If I let the Truck cool down I can get reverse back and I can drive the truck in drive for pulling a trailer. The truck has 149,000 on it.
Should I take it to a Transmission shop? This has happened two other times and in the last five years I brought the Trans back by changing the filter and fluid every 5,000 miles.
Do you think it might be a solenoid ? Answers will be appreciated.

I hate to say it but you would probably be wasting money on a filter and fluid you might be better off replacing it with a used one and C is 2 wd and K is 4 wd. You would have to get one for what ever your truck is 2 or 4 wd.