Dixon ZTR - how to tighten PTO belt?

I have a Dixon ZTR RAM 50 MAG (2006?? model). The PTO belt from engine to deck is slipping, and when attempting to mow high/thick grass, the blades basically stop. How can this belt be adjusted/tightened? It seems crazy to buy a new belt for $40-50 or more just because this one is very slightly stretched! There seem to be no idler or tensioner pulleys on this belt, and it seems to be entirely tensioned based on the engine and deck positions relative to each other. Thus when I raise/lower the deck, the belt is a bit tighter/looser, but always just a bit too loose for heavy grass. Can the deck be adjusted forward to tighten?

As an aside, how can I tell the year of manufacture from the serial number? There's no model number anywhere that I can find. Just a metal plate with the serial number riveted to the frame.


Thanks!

http://www.dixon-ztr.com/service-and-support/user-manuals/?query=Ram+50&types=O,I

Try above.

It is tensioned by 2 big springs on the linkage.
If the belt is slack then it must be worn.
The only other thing is if the engine mounts have slots where it can be pushed back to better tension the belt but I dont think it does

If this is you deck what I circled in red it the adjuster. Belts do not stretch they wear down on the V till they bottom out on the pulleys. if your belt is bottoming out no amount of tightening will fix your problem.