Surges when coasting.
 

The other issue with my pop's 87 6.9 4 speed is that when you lift off the pedal a bit, it is likely going to get to surging/lurching. Could this be a severely loose timing set up? seems like it almost feels equal to a super slack flappin' timing chain with broke tensioner would feel...
Brent

mine would do that occasionly.turned out to be a loose fuel line before the lift pump.

Yea, it sounds like it could possibly be air intrusion:-X13

have u check the clutch ?

Is the fuel tank selected at or near 1/4 full........ could be a broken fuel pickup in the tank.

Think fuel issues on this, the timing is gear driven and they last a long time.

The problem was fuel delivery related.... Yesterday I installed a rotary type lift pump, bypassing the mechanical. 10 new feet of 5/16th line and his surging is gone. Overall from idle to pulling load, the truck is 100% smoother now.
Thanks...
Brent