Classic/Antique Car Repair: 1968 plymouth fury 3 droptop, plymouth fury 3, high gears

Question
I have a 383 V8 engine I think Im have transmission problems. I got filter replaced and new fluid. Does this car come with a modulator valve or was it made without. If so will I have to get the transmission rebuilt or am I missing something here. When I start the car and put it in reverse is backs up fine. I put it in drive and it only shifts twice like it won't go into the high gears. I can manual shift myself going from 1st to 2nd to drive and it runs good. I have no idea what the problem is but I know its the transmission. Just seeing if I overlook anything before I go drop some big cash on this transmission rebuild.

                                            Thanks
                         And hopes to here back soon

Answer
Eric, this car is NOT equipped with a vacuum modulator. It does have a throttle rod running from the throttle linkage at the back of the engine to the transmission. It is a three speed transmission and will only shift twice on the way to high gear. First to second shift should occur at moderate throttle at about 20 miles per hour and the 2-3 shift should occur around 30-35. The linkage can be adjusted but the procedure is slightly different depending on the type of linkage on the car. I checked a 1971 Motors Auto Repair manual and it gives the proper adjustment again depending on the type of linkage.
Brad