Beautiful boat 

It just had a new transmission installed. Initially when I water tested..right after the new install...if you put the boat in FWD gear...the boat would go in reverse...and vice versa ( put in Reverse...boat would go fwd)

that was fixed....i now own the boat...issue is.

in Neutral...boat rev's fine and throttle is normal...(only using about the first 45-60 degrees of throttle range..revs well passed 4000rpm...)

when the boat is in gear...it has a ton of throttle play and will not get passed 32 mph...(3300RPM) ...(full 180 degree throttle from neutral position all the way to the floor...) its slow and lacking ...only goes to 3300 RPM ...

i've checked PP and it seems to be fine...anything else possible w the throttle play and lack of power while in gear? 

Sounds like your cables need adjusting. Give this adjustment procedure a try:

Gary S wrote: Greg here is a how to post from Alan 81nautique,on how to adjust your cables--- There's a procedure to follow for properly adjusting your cables. Give these steps a try and you should be good to go. 1. Disconnect cables at trans and carb 2. At the morse control disconnect both cables and rotate the brass pin connector so there is approx 1/8" of thread showing at the cable end. Reconnect both cables to the morse. 3.At the transmission, place the transmission bracket(the one that the cable attached to) in neutral. You may have to move it back and forth to feel exactly where neutral is but it should detent in the center of travel. Once you find a firn neutral connect your trans cable. 4. Step 4 is the magic. Go back to the morse control and with the transmission engage button in, move the throttle lever to the forward engage detent. Just move it forward and it should lock into the forward position firmly, stop whne it does so. Now go to the carb, adjust the cable connector so the throttle cable smoothly attaches to the carb stud without moving the throttle. You are done. This sequence works for me everytime with NO tweaking if you do it right. The trick is you must have the throttle in the forward (or Reverse) detent BEFORE trying to attach the cable at the carb.

If it works, then the installer should take note as well. 

Like they're saying, your gt40 has a throttle cable

Just substitute "throttle body" wherever you see "carburetor"  in the adjustment section that Pete posted 

Check that the cable is firmly mounted to the bracket on the engine too