Question about exhaust systems?

I have a 1995 Ford Bronco it has the 5.0l in it with just over 100k. and going up hills it just seems to bog out i have tuned it up. put new injectors in it and a new k&n air intake but still it no improvement. i was talking to a buddy of mine whos a mechanic and he said on older fords the cats get blocked up and give to much back pressure so it makes the truck hesitate. just wondering if anybody has heard of this and if i should hack off my cat and see if it improves i do have a new y pipe for the truck so if that is the prob i could just slap the new one on but if its not then i dont want to do all that work for nothing. whay do you guys think?