The TH350 and TH400 are legendary transmissions, but if you want overdrive for highway cruising in your classic C10, the 700R4 swap is the most popular upgrade. With a lockup torque converter and 0.70 overdrive 4th gear, it transforms highway fuel economy.
This thread is a complete 700R4 swap guide for classic C10 trucks: crossmember modification, driveshaft length, TV cable setup (the #1 failure point), cooler lines, and kickdown adjustment. We also discuss converter stall speed selection.
The JY PERFORMANCE Adjustable Trans Crossmember for 1964-1987 C10/C20 is specifically designed for this swap — adjustable positioning fits both TH350 and 700R4 without requiring frame modification.
Have you done the 700R4 swap? What TV cable setup are you using?