slipping already?
 

I have a 1996 Chevrolet Silverado 3500.with 230k on it.o/d is toast.And odd shift points at times.Should I risk performing transmission service(filter&flush)?

Money down the drain if you ask me, I have never seen one magically return to normal after a fluid change I would put the money towards rebuilding or replacing it instead @ $5 a quart for fluid and filter kit you would be money ahead not to do this imho.

I'm sorry I know this isn't what you want to hear good luck Mayhem.

cold advance solenoid
 

check it make sure its not bad. It affects o/d and shift points you can also lose o/d.

No this truck is not equipped with that stepper solenoid it's all electronic and that wouldn't affect the transmission at all if it was equipped.