Why does my 1999 Pontiac Sunfire has a long crank time ONLY during warm months?

Why does my 1999 Pontiac Sunfire has a long crank time ONLY during warm months? During Spring/Summer when it gets to be about 70 degrees or over, it has a long crank issue and I have to hold the key down for like 10 seconds before it starts. It usually ONLY does that when I start it for the first time for the day, then anytime after that, it starts like normal until it sits overnight or for a long period of time. BUT, when it is cold in Fall/Winter, it starts perfectly with no problem. It has been this way since I bought the car. It is a 1999 Pontiac Sunfire with a 2.2 OHV At. I have done a full tune up and replaced multiple parts that include fuel pump, pressure regulator, air intake temp sensor, coolant temp sensor, crank sensor, and cleaned injectors and intake manifold. Mechanics can't figure it out and I am about to replace the timing chain, o2 sensors and tps as money permits. I do not get any dtc when I use a code scanner. I am not a mechanic but know enough to diagnose and fix my own car I am just getting no where with this so any help or ideas would be greatly appreciated. Also the car runs great and idles great but once in a while it does idle a little funny for a few seconds but rare. Thanks in advance!