Greg,
Here's a link to the Trailer Life Magazine towing specs, going back far enough that you should be able to get an idea where you need to be, given that you already have a trailer weight available.
Somebody once said that you should try and get the biggest truck you can afford, because everything always weighs more than you thought! If you've already maxed-out on your trailers GVW, it might be better to increase the Gross Combined Weight (GCW) with the new vehicle, so you can keep everything manageable. Your 1990 R25 Suburban sounds a lot like the way mine was equipped, and with the 4:10 gear is rated at 16,000 lbs. GCW. The last time it went across the CaT scales it weighed just over 7000 lbs, all up! Passes everything but a gas station!
Good Luck with your search!
https://www.trailerlife.com/trailer-towing-guides/