I manage to get up about a 45 degree if not more slope on my ride on (on a river bank so not a long slope).
What width tyres are you running?
What air pressure?
I would firstly try dropping your air pressure, maybe as low as 5psi, trial and error.
Mine are quite wide, and they are flat (dead flat), haven't got round to pulling them off to fix, but the sidewalls on mine are stong enough that they don't come of the rims or distort with me riding on it, so really no dramas hence why down on the list of stuff to fix.
Secondly what gear, try using a lower gear.
Thirdly can you run up and down at an angle across the slope to reduce the angle your trying to get up.
Can you get up without mowing? You may need to mow down and then just drive up.
Hope this gives you a few more ideas.
Chris.
