Stall speed will go up since you'll have more torque. If you are keeping the same top end (heads, cam, intake) then the power isn't going to increase much if any, but the torque will increase. By keeping the same top end but putting it on a bigger bottom end you'll run out of air faster. A gear change may be required depending on where it was running out of air before.
Switching to taller rear gears will make the stall even higher so you'll have to keep an eye on it. 
CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
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