Having problems dehydrating apples

Hi guys

I have my own orchard and have started making fruit leathers. I've found the best way is to chop and cook the apples until soft, blend in a food processor with some lemon juice and cinammon. Nothing else. Then spread on a silicone sheet 0.3in deep. They go in my Excalibur 9 tray dehydrator. I usually run it at 135F (57C) for 10hours as recommended but I find 99% of the time the leather is simply too tough and thin. For some bizarre reason, I did one variety once (i forget which one it was), same procedure and it came out perfect. Not too much moisture that it will mould when stored, but nice a soft enough to be pleasant to chew.

I tried large apples vs small, and several different types (golden delicious, braeburn, gala, pink lady, worcester pearmain) to see if variety changed the outcome, but it didn't.

One person suggested I put apple sauce in with the blended apples, but I want to keep this super simple and not to have to make apple sauce. My plum leathers came out fine, and as i say, I somehow managed it once but not sure how as I can't repeat it.

If I run it for less hours, say 8, it' not dry enough. I know it will go mouldy.

Any suggestions?

Thanks