Kubotal MX4800 HST Stalling

[4beatg8]

My 3 year old MX 4800 HST has started stalling on inclines and when I try to push a round hay bale or scoop dirt.
Runs fine on flat ground with the bush hog, etc. We've replaced the fuel filters. What else could it be?

 

[jyoutz]

Have you checked the air filters?

 

[Russell King]

From what little you stated I would look into the lift pump if it has one or investigate the fuel flow at various points to locate any blockage