Long crank before start

Here is the deal, I dont drive my truck very often because I have a company vehicle. Usually drive my truck on the weekends. When i go to start it up after it sat for 5 or so days i have to crank for a long time and sometimes it takes two tries. Its not cold out and I just did an oil change, it seems as though fuel pressure might be leaking off? Once it fires it does just fine and starts right back up. This has me puzzled has anyone else experienced symptoms like this?

Could be more along the lines of hpop oil pressure. If you can, get a scanner and watch icp while trying to start. You will need over 500psi for it to try and start.

Would that cause a long crank just when cold or every time?

Not every time but it's a step to finding the problem.

Check it for codes, could be ICP, glow plugs. You really need to scan it, that will send you in the rite direction.