Wasted an entire day wondering why the heck graphics weren't being loaded. I examine RAM, the data is there. I look at the code in a debugger and it's indeed executing in the subroutines it should. I look at the code that sends the commands to the video hardware, pointers are OK, then I step and the loop is running, yet somehow the video hardware is ignoring them... wait a second, did an instruction just get misassembled?
cmp.l a4, a5
cmpm.l (a4)+, (a5)+
Huuuuh not only it got converted to the wrong instruction (CMPM instead of CMPA), where did the assembler get the idea of adding postincrement?
Any chance the V coordinate is flipped upside down? (i.e. top-to-bottom vs. bottom-to-top) I don't think there's much you can do if the two models are using different conventions other than to flip the texture itself.
Maybe showing a screenshot would be useful? (EDIT: especially since "totally gray" sounds more like the texture isn't being used =P though that's more likely to show white?)
I suppose another reason why high-end equipment has RCA is that, well, it works with just about everything out there. That's pretty important when for whatever reason you can't go and make your ideal setup.