Yes, it does affect tension. There is less belt tension with the deck in the highest position on the 2000 Series in general. The 38 and 42 decks, particularly.

Is there anything I can do to address the loose belt at high deck setting? New belt, or spring?

Post some pics showing the top of the deck, the belt, the pulleys and the spring so that we can see what you have going on.:bigthink:

The rear lift arms are angled from top to bottom towards front of mower so that as you raise the deck it moves up and back slightly to maintain tension on belt
If your deck is not moving backward as you raised it the first thing I would check is the front hanger , second would be the deck drive pulley tension spring
Photos would assist

Well, it took me forever to even get out to take a pic and not sure these will even help but here’s what I’m working with…

I don't see any obvious problems that would cause your problem. Just make sure that the tension-er is nice and free. The item in the red box.

Sam Mac,
I went to mow and the deck belt slipped off again. Every time it happens I notice the tension spring has also come off it’s post but assumed it was because the belt was off the pulleys…now wondering if the reverse is the cause. I dropped the deck and yes, the tensioner is moving freely and I closed the end loops on the tensioner pulley spring just in case. I also cleaned under the deck while I had it down but also found I’m due for a new belt. Is this cause or effect?

You definitely need a new belt. While you have the deck off check that the belt tensioners pivot freely.

Put a new deck belt and pto belt on today. BIG difference in tension on the deck belt! Guess the old one had stretched? Did a quick mow with it. All is good so far.