Hi,
I have been getting code p0449 for a while now and when I get gas my truck acts like it dont want to crank but only when I get gas. I have replaced the purge valve and also vent valve solenoid.

Has anyone also had this problem and could tell me what else it may be?

I don't have any experience in OBD 2, however here is the techinfo article from this site on this code:

https://www.gmforum.com/obd-ii-troub.../p0449-285608/

One thing that is worth noting is that it appears the issue is electrical, and under normal circumstances shouldn't affect drive-ability.