Take a look at every place a rod end goes through a hole, and the pivot point where the do-hickey attaches to the side of the block.
It would be best to remove everything from the truck so that you can carefully inspect for wear.
There are many pivot points on the gas pedal linkage assembly. If you have some wear on all of those points, they can add up to a lot of resistance in the pedal returning.
You may want to remove the spring and move the gas pedal up and down to see if the rod is passing through the toeboard for the full travel without dragging on the toeboard.
