case ingersoll model 224 problem

[a_sannine]

my case ingersoll is made 1986 , the only problem it loose power in full speed in high range forward only , especialy on hills , and i feel the engine stressed , while it smokes tires in reverse high , low speeds good , only high speed forward , loose power , what should i check , what's going on here , all oils new and good
thanks
any help will be great , please email me at a_sannine@yahoo.com
many thanks again