Potential Tire problem?

Yes, temp rise causes pressure rise. And also modern tires will have slight Waves in sidewall

I am worried that they are underinflated now

Your tires are under inflated. You should not let air out. Inflate them to your desired pressure when cold.

You should have never reduced the pressure. The pressure will be below your set point of 80 when the tires have sat all night. Air them back up to 80 and don't be concerned. Warm air (inside) expands), all normal.

A slightly rippled sidewall is of no concern either. Belts slip in the carcass and most all tires will exhibit that at some point, disregard it unless there is a beak in the sidewall rubber, then you have an issue.

Air the tires back up tomorrow morning when cold and continue on.

If you originally aired them up in Indiana, you will pick up 2-3 psig just due to the higher altitude in Colorado.

If you set them at the correct pressure cold, they will go up in pressure driving, especially at high altitudes and in hot weather. Tire correctly inflated cold will never increase enough in pressure to be a danger. Never 'bleed' pressure out of a hot tire.

I've seen my tires set at 80psi @73 degrees rise to over 100psi when the temps raised to 95* and I had been towing a FW for 300 miles. The pressure rise is actually calculated in the tire design.

Doubt you've done any harm. As said, just air up in the morning and travel on.

Thanks everyone this makes me feel better. I will Air them up before I hit the road this morning.

At least we didn't get into the Nitrogen debacle / debate. Whew...

^Right?

Regarding tire inflation, you'll be fine either way. So you had 90 hot at altitude and probably couldn't tell the difference between that and 83 or 77psi honestly.
Max load according to the tire is 80psi "cold" right?
So what's "cold". Sunny side of a truck parked in Phoenix in July? -30 in Fargo?
Point is as long as you are not grossly over or under inflated the rest is either personAl preference or being aired up for the load in general.
Good question though.
I'm in the personal preference category where I try to tailor my psi to the load, but I also rarely, if ever check pressure between changing it (on vehicles with no tire monitoring).