I don't think the aluminum stock tips can be welded to steel pipes. Since you live in a "snowy" climate, I'm sure road salt has caused the tips to be rusted on the pipes. Loosen the clamps all the way and tap the tips with a hammer, at the clamps.
Some type of grinder (bench/handheld/Dremmel, etc...) with a wire wheel will clean up your tips real nice.
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Bobby
Died 5/1/08, resurrected 5/15/08
ASCD SD hood, 17" Bullitts, Overkill PCM, 3.4" Pulley, NGK TR55IX, K&N 9" cone filter, JimmyC D/P, U-bend removed, Flowmaster 40 series, Hooker big bore tips with resonators, S/B brake lines, drilled/slot rotors, GMPP handling kit, KYB struts, F&R strut supports, HID's, LED's, 2.5" Air Dam, red GTP overlays on custom badges, white rear insert.