Do you have one of those Smartsteer Mags?
I run a Mag but it is not a smartsteer unit. I also get spinning of the uphill wheel when running sidehill. Nature of the beast. Shift your weight or walk behind the unit until the slope evens out. Let a little air out of the tires (speaking of which are yours fluidfilled?)
7x14 Stealth SE Enclosed with 48" side ramp
2013 Gravely Pro Turn 260 with Kohler 26.5 EFI
08 Toro Z400 48" deck, 21HP Kaw with EZ Vac twin bag
09 Exmark Turf Tracer HP 36"
21" Toro SR4 Super Recycler
Stihl KM90 Kombi w/ straight shaft trimmer & tiller heads
2 Husqvarna 125B Blowers
Turfco XT5 Aerator
Turfco LS-22 Overseeder
EcoLawn 200 Applicator
I can do all things through Him who gives me strength.