I suspected that it was a problem resistance but I didn't know if it was a reasonable answer for my problem. I own a custom copper solo trumpet by Calicchio. It's actually the horn on their website (unplated). It uses a 9 leadpipe which is the largest they have and largebore throughout. It wasn't until 2 days ago that I realized that my powerpiece 5C used a #25 throat whereas my old Parduba 6 (which I used for 10 years) used a #27 throat and thus smaller adding to SOME resistance on a trumpet that was already so large. I didn't think about using a shallower cup, though. I can't even speculate on what cup-size a Parduba 6 was! They have such a funky style it's really a hard call on that one.
The one thing I do realize is that the 5C, even with tons of correct practice, still feels huge to me. It feels like I can move around all over the mouthpiece and still not find the right placement where on the Parduba 6 it wasn't as large so it had a smaller "sweetspot" to me and easy to find on a consistent basis. Thanks very much for your replies. I'm in talks with my mouthpiece maker for a mouthpiece that is closest to my old Parduba in size especially to the width of the rim since Pardubas have wide rims for cushioned suport.
I didn't think anyone would be able to help me so I really appreciate everyone's help. I know one day this experience will give me the insight to help another young trumpet player that may possibly be going through the same thing. Thanks again!