98 K1500 5.7 runs perfect but starts very wierd..Need help!! Long time no post! :)

On my 98 K1500 5.7 automatic this starting problem has progressively gotten worse. Usually when the truck is cold I will get in it and start to crank it up and it sounds like it's going to start so i let off the key but the RPMs will kind stay real low and the truck will hesitate then finally crank up and idle. (idles a LITTLE rough). but I drove about 15 miles yesterday at about 70mph the truck ran fine and I stopped and parked the truck for maybe 10 minutes and when I got back in it and tried to start it, the truck cranked and cranked for like 3 full seconds then it finally started (barely). I don't know what this could be. I replaced the cap, rotor, plugs, wires not long ago so it's getting spark. The starter is fine I can hear it spinning fast. It should be getting air so my guess would be a fuel problem but the pump was replaced about a yr ago and it runs fine once it's running????

Any help is appreciated and sorry for the long post.
-Nate