Any progress on this?
I don't know how your engine power is robbing you, and turning the IP up might work. What I suggest can help you/all of us get more use from our tractors in matching the load/work to its size and is also applicable to any size tractor.
1. Check the hydraulic pressure and bypass at the spool to ensure you have proper psi giving the correct lift capacity.
2. A tooth bar would aid in braking up hard soil and dig or fill your bucket easier.
3. Added weight would permit greater engagement with the earth and pulling power.
4. Ag tires for agricultural work, R4 for industrial use.
5. Working in lower/low range allowing full horsepower to be transmitted to tractor (Requires more time, easier on tractor).
6. Working in a higher range with lighter/looser materials to gain momentum/inertia with the weight of tractor to fill bucket or traverse terrain (Can damage tractor and property if you have miscalculated).