I have the original trans on my car that I sent to get rebuilt because eit was sleeping and was leaking I took off the transmission myself and installed it back my self but I only feel it change gears twice once when I'm going at 15 to 20 mph and the other one around 30 to 35 mph but after that I feel like when I'm driving over 55 or 60 I feel like the car is running on high gear I feel like it should change into one more gear I called the place that rebuilt it for me and they told me that its a three speed trans first speed is at one and two and then goes two and three that is consider a three speed trans does that make sense to anyone I want to be able to drive on the hwy but I feel like I'm going to blow my engine or trans because it feels like I'm forcing it. by the way it is a 1967 Cadillac deville convertible with a auto 3 gear box transmission I think its a 400 trans I could be wrong I know it is the original one.

 

TH400 is a three speed transmission.

You drop the shift lever into Drive. You've engaged first gear. Transmission shifts into second. Transmission shifts a second time into third or "high". Two shifts, three gears. Compared to a modern "overdrive" automatic, the engine is going to sound like it's running fast and that there should be another gear. There isn't. That's the way they're made.

HOWEVER, I suspect you should also have a two-position torque converter; and you might feel the torque converter stator shift position. It's often compared to a very soft gear change.

1. Did the transmission have the dual-position torque converter? 1967 was the last year of that feature, and not all 400 transmissions got it--No Chevrolet TH 400 had that feature, not all Pontiacs had it, not all Oldsmobiles or Buicks had it. Some did...some didn't. It was expensive to make, so it only went into the higher-priced, big-engine vehicles. Which is a shame, because it was the low-powered cars that really needed it.

2. If the transmission originally had the two-position torque converter, did the shop that overhauled it steal that from you and replace it with a single-position torque converter? The throttle linkage should have a pair of electrical switches, one for "passing gear", the electric kickdown solenoid; and another switch for the torque converter. There will be TWO wires going to the TWO-terminal connector on the side of the transmission.

3. If you still have the two-position torque converter, and it's never switching to the high-speed position, the engine will rev more than it should, fuel economy will be horrible, and the transmission will run hot.