Most 5.0 Mustang AOD's shift 1-2 at around 4700.
You can adjust that somewhat by upping the tv pressure.
Look at the TCI website for info on how to do that.
The stock setting is around 33 psi with a lukewarm trans
and a gauge block holding the tv cable out a specific amount.
You need i.e. a decent oil pressure gauge attached to a port
on the right side of the trans
to check that.
You can set the psi up to 40 which will help increase both
shift points and firmness during harder acceleration,
as long as you keep the at-idle psi with no gauge block
at 5 psi or below.
Also, has your governor ever been changed?
There are 3 diff gov's for AOD's, with the Mustang
one being the highest. Maybe somehow or other
you got a lower rpm governor?
With a Baumann shift kit, you can make further adjustments
to your shift points.
89 Linc Mk VII LSC mass air w/A9P; 95 351 Lightning shortblock, 1.9 Ebrock heads, GT40-351 lower w/match Explorer top, 70mm mass air w/30 lb inj's, TF Stage 1 w/1.72 Crane rockers, 1-5/8 ceramic shorties, 2-1/2" Dynomax catback, 3 row rad, Ford blue hoses & wires, remote trans
filter & plate cooler, 2500 lockup stall, beefed AOD, shift kit, 3:55's, 96 Cobra 17x8's, 99 Stang bolt on scoop. 4R70W, 2600 stall, Baumann TCS soon.