Increase pace as a power walker?

I’m a fairly new OTF member (~20 classes in) and need help on how I can increase my speed as a power walker. Right now, I can barely do 2.8/3 mph at 3% as a base pace, and even then I’ll be in the orange zone within a few minutes. I normally start on the floor and end with the tread so not sure if that makes a difference. A few classes ago, a coach told me I need to be going at least 3.5mph. Any advice on how to get there? I try to do 3.3mph on all outs or even shorter pushes but I’d really like to be able to increase my base pace without feeling like I’m dying after a few minutes. Not sure if increasing my speed is a better option or to up the incline. Any and all advice is appreciated, thanks!!