Mine is both top heavy and bottom heavy. When it's full it doesn't bounce. 3/4 down to 1/4ish it tends to bounce. Then from 1/4 down it's pretty stable again. I think I have a 40 gal tank but I've never been daring enough to run it that low. I'm pretty sure the most I've ever put in is 32 gal.

And 38 gallons in a Tundra? Chit man, that's more than my long bed gas guzzling v-10 F350 used to hold...