If it still tilts back fine, it's probably in the valve or even the linkage sticking. Most the time the valve body is covered in a bunch of dirt so it's easy to hang up or get dirt in it. You could put a pressure guage on it to check it to be sure.
It could happen, but not common for both cylinders to go bad at the same time.
BTW I hate working on forklifts. You have to bend over almost all the time no matter what your doing to 'em.
And I think your 60' times will be faster with the forks tilted down. lol