I recently purchased a used 1994 Wheel Horse 13-38 HXL Lawn Tractor, Model # 71191, Serial # 4900314. The mower has difficulty going up an incline of less than 20 degrees with a rider. The engine remains at full power and does not draw down. Disengagement of the blades does not improve the performance. Performance appears to degrade as things warm up. I'm led to thoughts of the transaxle. Are there adjustments that can be made? Fluid to be replaced or added? Tricks to consider outside of loosing weight or replacing the transaxle? I am not mechanically inclined but I have access to individuals who are. Thank you for your thoughts.