Can't offer much advice specifically for the 8.1 but I have it's little brother. I've read to the bottom of the internet for performance upgrades and came to the conclusion there isn't much 'bolt on' stuff that's worth the money.
A tune from Blackbear performance is about the only thing showing good results online BUT it's from the stop light to stop light crowd, not guys towing. I'm not even sold on the CAI and exhaust.
On the other hand, the 8.1 should pull 8000 around like nothing. My 6.0 does decent with 9000lbs. I wish I had the big block actually!