It's prob just a long gear and you don't have enough power to get over it, is it like a rev limiter, or just climbs extremely slowly?Yes, I noticed it was shifting odd while it was in auto so I tried manually shifting and that’s when I couldn’t get it over 3k rpms in 4th gear. Even with flooring the gas pedal it won’t go over 3k rpms, but only in 4th gear.
I agree, prob has some trans code storedThe GT has NO issues going over 3000rpm in 4th.
It sounds like some sort of soft limp, odd that it's only one gear.
Scan the trans, see what codes you've got going on. Engine codes could be useful but probably won't cause this