The button on the shifter is used to diable the Torque Converter Clutch, NOT 4th gear.
You will still get three upshifts, even with the Torque Converter Clutch disabled.

Rob, what year is your GL, is it a Zetec or a Duratec, and how many miles do you have ?

When was the last time the transaxle was serviced ?

Pete...

98.5 SE Sport Duratec ATX (P66L)
Black Clearcoat on Greystone
DOB 11/21/1997
DOP 12/25/1997
PIAA 510 Super White Driving Lights
SVT CAT-BACK EXHAUST (No Resonator)
DiabloSport Chip (LPQ4) - Engineered To Raise Hell
Too many other mods to list...
Sounds sweet, runs quick...
Crazy Horse Dyno @ 121.4 WHP/129.6 TQ