Is 75W-140 too thick for a Merc outdrive?

I use Amsoil 75-90 Severe gear

It'll work just fine. Touch heavy, but it'll work. Best recommendation is a 75w-90 or 75w-110

Dang! I use Redline Severe Gear, 75-250. 705 HP with XRs in a '02 38 Lightning. I'm moderate on the sticks. No holeshots but lots of WOT. Longest was for 35 minutes. An upper gear broke at 145 hours. The other had pretty good pitting. I'll change them at 100 hours now.