Engine Performance problem
1996 Dodge Truck V8 Two Wheel Drive Automatic 56K miles

When auto is left (unstarted) for more than an hour it takes apprx. 10 secnds of cranking for it to start. Once started it runs fine. When shut down and restarted at once there is instant start (like it used to be). Would it be advisable to change out the regulator/filter only (diaphragm may be bad) or the whole expensive fuel pump module.
All parts are in tank,Right?

Thanks:
Dave