Engine sputters only when cold

Hi all. I recently started having trouble with my '99 Tahoe Z-71 (116k miles) and was hoping for some useful insight. When I get in the truck to go to work in the a.m. (after sitting overnight at about 60 deg F) it runs really rough on acceleration (either slow or hard). But when I get in it to go home at the end of the day (after sitting in the parking lot at about 80 deg F) it runs trouble free. I immediately replaced the fuel filter (which I do on occassion anyway) as my first course of action but there was no change. Then I added some dry gas thinking I had condensation but that didn't help either. Any ideas?