Agreed.
@mwalker4 any idea if that truck has the 4L60E or the 6L80E transmission. The 6spd has a lower first and a higher 6th than the 4spd it replaced. The 6L80E also has a higher static torque rating so it will handle a bit more abuse. The 4L60E is based on the old 700R4 (but with electronic controls), which honestly isn't a terrible transmission, but is showing it's age at this point.
Overall, I would just accept that the 5.3 is a bit of a screamer. It's relatively small by US V8 standards, and with the heads/cam package that GM puts in it, well, it likes the revs. Don't be afraid to let it get up there in the rpm range. "Screaming" at 4k isn't going to hurt that motor a bit.
Looks like you're running the stock sized tires/wheels, so no real issues there. The Avalanche is based on the suburban chassis, and is a bit heavier than the pickup. Honestly, it's a fine tow vehicle and should handle that boat no problem. Just take your time and slow down.....Towing above 75mph is gonna be hell on your trailer bearings and tires anyway, so budget a bit of extra time and enjoy the ride eh?