Default [Q] booting from fastboot problem

so I've been playing with the options long enough that I'm not satisfied with what's available, so I figured I'd try customizing a kernel myself. I think I have a pretty good idea about how to make that happen, but I've run into a problem on testing. I can't seem to boot using fastboot boot ______. Whether I'm using the twrp recovery boot, dd of mmcblk0p35, or the freshly split boot.img(ramdisk and kernel), fastboot responds with ok, but my phone sticks on the bootloader fastboot usb screen, requiring a hard reboot. Is the only option to use the any kernel zip? or am I just screwing something up?