1998 GMC k1500 5.7ltr starting

Hi all.

I have a problem starting my truck.

Specs: 1998 GMC Sierra SLE 5.7 Auto Tranny 4wd
140k mi a/c

Symtoms: Engine will not start when it has been sitting for an hour or more. Once running its like new. No loss of power, gas miliage etc. Will start up with just a short turn of key after shut off. On warmer days I can get it started after several cycles of turning key and fuel pump charging the system, otherwise I have to give a short squirt of starter fluid down throttle body and then every thing fine.

Recent repairs:(past year): fuel pump/ filter and pressure sensor at tank, distributor, intake manifold gasket, water pump, alternator, and recent general tune.

Any insight would be of help