brake shift interlock

[tfpary]

97 suburban - k1500, 5.7, 4l60e.  Last week it was colder than snot out (-25 F) - the truck started fine, but was impossible to shift into drive until the interior warmed up a little (maybe 10 minutes - so it didn't warm up a lot). The shifter acts just like you  aren't stepping on the brake. Wont move an inch. I tried various combinations of wiggling the shifter and key switch, and never came up with anything that worked reliably.  Any thoughts? It really sucks to be stuck waiting for 5 or 10 minutes, but at least it starts!

Thanks!