No power up hills/engine bogs (I'm at a loss)

[BigDaddy325]

This will be my third thread trying to figure out this 1994 EZGO.

The cart has no problems for the first 5 minutes of driving, but soon after the power seems to bog down. I've proved this by immediately taking the cart to a hill, going down, and making it back up at a decent speed.

Withing 5 minutes of running, slight hills slow the cart down, and steeper hills are impossible to get up. On flat ground I'm getting around 13mph, but on hills (If i can even make it up) I'm averaging like 1-2mph.

One of the only things I can imagine it being at this point, is the clutch. That doesn't explain why everything is fine for the first 5 minutes, and why I seem to lose power afterwards. It's not like the belt is slipping (cool to the touch), the engine rpm's take a dive meaning the clutch only engages about halfway.

Things I've Done:

New Carb
New Spark Plugs
New Drive Belt
Fresh Gasoline
Valve Tune
Compression Test (175psi on both)
Choking while driving kills the engine
Set up gravity fed gas directly to carb
Running the cart with no air box (performs slightly better)
Shortened Throttle Linkage
Adjusted Governor
Adjusted Air/Fuel ratio knob

The only other info I can offer is that the plugs after running are carbon fouled. Black, matte soot covers them.

Please help!