Need GMC Engine Help!

[5Tractorguy]

So I've been having trouble with the GMC 351 V6 in my 5000. It's been lacking power incredibly badly going up hills, bogs down without any load on the truck bed. I can mat the accelerator uphill and there is no difference.

I've done everything to the engine except for the distributor cap. I've cleaned the cap contacts and checked the spark and it is good. Points are set at .016, timing is set at 5deg, new coil, valves have been adjusted, cylinder compression is 120psi, air cleaners clean, fuel pump is good, fuel filter is new, etc...

It has the "Handy Governor" thing on there too. Removed it and set the spring by the GM book (maybe remove it all together)?

So right now I'm leaning towards either timing or too much fuel, but I'm not sure.

Any ideas??? I'm using it to haul tractors to a show this weekend so I gotta figure out something!