G1800 mower deck height adjustment problem

[bstauss]

I have two recently acquired G1800's with 48" decks. Both decks are out of whack on the height adjustment, with the front rollers on the ground and digging little trenches. I was able to properly adjust the front links on one of them to suspend the front of the deck about 3/4" off the ground, with the rear deck wheels on the ground. The other one, no matter what I do, I can't get it adjusted. If I get the front rollers off the ground by adjusting the front links shorter, the entire deck is off the ground - I made sure the hydraulic lift was "down". I think I have a lift linkage or lift hydraulic cylinder problem, but am not sure how to trouble shoot it. The deck does go up and down, not sure if it is the full range of travel. If the front rollers are on the "high" setting (top hole for 3" cut height), the front of the deck doesn't leave the ground. Something is wrong. Can anyone suggest where to look next? Thank you.