I'm not sure I would worry about the rpm's. I have a 4-107 and I average around 60 lbs at any speed. There might be a slight dip at idle, I'll check next time I'm out. 2200 is the top of the torque curve for that motor
. I know that it is not unusual to run these motors at 1800 for their entire lives. 80 lbs seems high to me. Start with the simple things and trouble shoot the gauge and sender, then move on from there.