I don't know about the first to second shift,......BUT, the shuttering in reverse is definitely a clutch pack problem....I know that, because that's what exactly happened to mine...
I talked to Brian from BTS about it....[that was several years ago], and I had a BTS transmission put in....His cost my run upto $4000, but that is a good deal for what you get....other than that, you may try a Ford 4R100 ""HD"" rebuild....I would definitely not go with a local transmission shop rebuild....Check you tranny fluid....It's most likely black, from the wear of the clutch pack plates....Mostly likely you in for a new tranny...PERIOD