where did you source the parts? might be some poor repros around - yes Goodmark has the TF parts, and most FLAPS suppliers use them [Cross Canada Auto Body up north] .... another supplier is Dynacorn - both make parts with reasonable fit, but I've never seen a patch that didn't take some adjusting to the vehicle - for these ol trucks they're using dies reproduced from drawings or good original parts, not like the parts for later cars, some of which are from existing era dies
I've had no problem with the step/rocker pieces from Goodmark/Cross Canada - haven't used the repro corners, but one truck I patched with good corners cut off a scrap cab took as much fiddling as any repro patch I've used

Bill