Put larger tires on to get more height.
3" is close to max height. Does it come up against the frame at its present adjustment?
I had the same issue with my 3520 with 72 inch deck. I pulled out the manual and looked a few things over and noticed the dealer did a crappy job setting the deck up. The lift was adjusted wayyyy incorrectly. I had to take up a lot of slack and now the deck lifts up several inches higher and comes within an 1/8 of an inch of hitting the stops. Thats where it is supposed to be according to my manual. Maybe you have the same issue. Look at your mower deck manual. Takes about 10 minutes to correct the issue if this is your problem
More info please. If there is a gap between the mower "uplimit" tab and the frame when the mower is in the full up lock position, why don't you adjust it?
All you have to do is adjust the two lift mechanism turnbuckles until you get to within 1/16 of the frame. Then you should have the full range. For what it's worth, mine won't mow at the advertised 6 inch height unless you have it in the locked up position, but it does have a reasonable range when adjusted correctly. (Note: I figured it out and adjusted it myself after the dealer couldn't get it right in two tries.)
Before I adjusted my links length, there was a 4" gap, now there is a small gap, mower is set right for travel, but the highest I can get the dial knob to go is again about 3 ". There is an obvious compromise between high travel setting (Where it just hits the frame) and a lower cutting height in the middle of the dial. Do you have the 3 point hitch link with the threaded yoke?
VP
I have the independent lift kit, but I think the adjustment is the same. On mine, there is a pretty big gap between the lock setting and the highest mowing setting. If I remember correctly, the highest setting cuts a little over 3" and to get a 6" height you have to lock it up. I mow with the setting in either the highest setting or the next to highest. The areas I mow are pretty uneven and I like to leave the grass fairly high. To use the lower settings on mine you would need a smooth lawn and like to mow short (which a lot of people seem to like).
It sounds like yours may be set up the way it's supposed to be. If you look at the cams on the height setting knob, you'll see that there are very large gaps between the highest settings.