Is that Pro Shot similar to Hoppies gun cleaner? It sounds and looks fairly easy. This truck ran good with no issues before.She has just been sitting for a while. It definitely got my attention when it fired up and I was so releaved when the shut off worked! I thought maybe she was going to run away on me and air condition the block!
Pro Shot Copper Solvent IV is far more effective than Hoppes 9 or other types. Both on firearms and engines/parts. And because it dissolves in water, it is easier to use.
I used it for just your problem a few years ago. Took all of 15 minutes. Had the EXACT same problem on my MEP-002A generator's injection pump, an Ambac model which is a direct descendant of American Bosch (A-B became Ambac in the 1980s). Again, this solvent worked.
I've cleaned diesel pistons with this solvent using nothing more abrasive than a Q-tip. Same with gasket surfaces, Bosch injectors soaked overnight and were perfectly clean.
Just remember, it dissolves copper. So rinse with warm water if it contains copper (brass/bronze) and then oil. It burns on cuts and broken skin plus it will remove all natural oils so wear gloves. And it also works well on firearms. Best solvent for cleaning AR15 bolt carriers.