1997 Chevy Truck 1997c1500

T have a 97 c1500 with new feul pump, timing chain. When truck sits for a day or so it will not start, it has good spark and has fuel. Once it sits it will turn over but takes a long time to start- 3 days this last time- it gets loaded up with fuel sometimes and backfire but won't start. It only does it in the morning if it sits all day and I try to start later in the day it will crank right up most of the time. After I get it to crank in the morning when I start to drive off it has some hesitation but then runs fine all day. Also have noticed black sutt/ residue on rear fender where tailpipe exits truck. Thanks for you time.