JLG 26mrt scissor lift Drive issues.

I have a 1998 JLG 26mrt dual fuel (gasoline-propane) scissor lift. The issue is when I start either engine the drive system will not function until the engine has been running for at least 15 min. I have to run the lift up and down, and steer the wheels back and forth numerous times during the 15 mins until the engine is warm. Once I have done that it drives fine for the rest of the day. I have to do this every morning. I have changed all the filters and fluid, check the power to solenoids, and replaced the control joystick. I hope there's someone who may know what the issue is. Thank you.