98 Isuzu Rodeo not driving in first gear.
 

Hello
I have a 1998 Isuzu Rodeo 2wd Automatic Transmission the 4L30e. It will shift into reverse just fine and smoothly. It will drive in winter mode. What it will not do is drive in 1st. When put into drive without winter mode (forced 3rd) it will make a humming noise and have no power. Now when I get it pushed past 1st it will engage 2nd and transition to the other gears and operate just fine. I checked the fluid while at operating temperature and in neutral on level ground, and it's full. It is not sending out any codes. Does anyone have an idea as to what is happening and how I can go about fixing it. Your help and advice is greatly appreciated.