"my level of play drops when I get to final tables"
You mention mental fatigue, so that's one aspect. The only remedy that I can think of to this situation is not playing if you feel you can't finish the tourney in an alert state. Alternatively, you just need to learn to play through the fatigue. No easy feat.
But are you analysing you game afterwards? I don't mean really in-depth stuff, but just a general sense of where you might be going wrong.
Once I hit the final table, I get aggressive and looser when in position. I'm looking to steal blinds (bec. they are usually substantial) and I'm seeing more flops if possible. I just feel that one needs to change gears at the final table. Sure, laddering up is a consideration, but I think controlled aggression yields more. But such a strategy calls for more mental clarity! - so might be much help to you now
My problem is that I'm too nitty before the bubble.
Anywho, keep working on your game and you'll probably see improvement on the final table. Everyday I keep working on mine, but sometimes I just need a break in order to restore the mental batteries and allow the lessons to sink into my feeble brain.
good luck