Try advancing the timing a little, or do a fuel pump output volume test. It's possible the torque of the engine just isn't up to the load you're putting on it, but if that's the case, there's something seriously wrong that's limiting the engine's power. It should accelerate in third gear smoothly from about 15-20 MPH or more.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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