I replaced my blown 93 d150s trans(a518) with one from a 94... All I needed to replace was the input shaft. The trans shifts fine under regular driving but when you floor it to pass it's hangs up in gear and feels flat . Also going up hills it dogs it up and on the highway it struggles getting to 70... Fluid is correct atf +4 and level. can the TV cable be adjusted on the 318 magnums? Is this a solenoid failure? How can I get the truck to run accurately again?

I'm not sure what the problem is in your case, but I don't think your truck should have solenoids. I think they started in 96 when everyone went to OBDII. It should still be a straight juice (hydraulic) transmission. Why did you have to change the input shaft? Was your original tranny a non lockup? Is so, why didn't you just change the TC and all and make it a lock up?
I replaced the solenoids in my 96 tranny cause the symptom was because it would hang onto gears like it was in eternal kick down mode. I would have to take my foot all the way off the throttle to make it shift, sounds like you have a different problem

The TC was the one with the trans the shaft I changed was the one on the driveshaft cuz the splines were different.. I'm pretty sure there's a solenoid in it... Behind the trans filter... It does hang up at times. When I go to accelerate it should do so smoothly... And not rev high with out moving hardly faster

Is the trans downshifting when you floor it and then does it upshift when picking up speed ? Ron

I don't know if it is the cause of your problem, but the tv cable can be adjusted. There is a button where it latches onto the throttle body and it slides to adjust length. I don't know if they have different ratio levers on the transmissions like the older 727s, but it might be worth comparing the new one to your original also.