HRX217 slow ground speed during cold weather

Hi, my HRX217 has slow ground speed during cooler weather. I purchased the new mower in July 2018. I keep the ground speed control on the fastest setting all the time. The ground speed cable and the drive clutch lever cable are adjusted correctly. When temps are above 65 degrees, the ground speed is normal. When temps are cooler than 65 degrees, the mower ground speed starts out really slow, as if it were on the slowest or second to slowest speed setting. As I use the mower, the ground speed will slowly get faster, as if the transmission needs to warm up. The transmission makes a groaning sound until it warms up. After about 10-15 minutes, the ground speed is faster, but not as fast as if the outside temp was 65 or above. The local service tech at the dealer only suggested adjusting the ground speed lever cable and the drive clutch lever cable. I am no mechanic, but it is almost like the transmission oil is too thick or something when it is cold. Any help is appreciated.

You are not the only one who complains about the speeds.... Yes the oil gets thicker when it's cold.....You will have too find a way to get the tranny warm before you go out and use the mower....

Keep inside the house overnite the night before ???? Heating pad wrapped around the tranny for a few hours ????