Can't find what rear springs to get

[swathdiver]

I can't seem to find an answer to the correct rear springs to get...
2003 Tahoe 4WD LS with nivomat premium ride suspension but I'm converting to a standard shock and spring setup. I installed 4 monroe reflex shocks. I have seen the bilstein conversion springs but people are saying they have too light of a spring rate. Right now with the nivomat shocks removed, the rear end squat is massive and 100 lbs of cargo in the back makes the rear drop way too much. On bumpy roads the rear seems to be floating around all over the place. I am looking at carid.com and found two spring sets:
16" free length 1040lb load rating spring (45H2165) and
17.2" free length 1300lb load rating spring (45H2164).
Both have an installed height of 11.5". No idea which one of those, if either I should get.

Dan, what did you end up doing and where did you get the specs for these springs?

I know now, that my stock rear springs are the 25783733/45H2164.

@Snowracer1000