The tube coming up from the lower intake is carrying hot EGR gas, and you want to ensure whichever tube you have here is properly fitting and such. The plastic intakes can warp/fail over time if this isn't done right.
Aftermarket fix (extra work options):
block EGR tube on rear exhaust manifold so this hot air isn't pulled into your intake, and cap or leave open the rear metal flex tube (EGR's not a useful method of emission/mpg improvement anyway)
plug the 2 coolant passages in the lower intake meant to circulate thru the throttle body (freezing open blades aren't an issue, even in Minnesota or further north, and this just provides another leak opportunity)
replace lower intake gaskets with the aluminum ones, if you haven't already (this is the #1 longevity issue on 3800's, and easily fixed)
A forum community dedicated to all General Motors makes and models owners and enthusiasts running the 3800 series engine. Come join the discussion about performance, modifications, classifieds, troubleshooting, builds, tunes, superchargers, maintenance, and more!