I'm from Colorado, and you are the first person I ever met that said there were any downhill stretches on the trails.

First,I would eliminate the easy problems. I'd suggest using trekking poles,as they really help take the strain off the feet. Slide your hands up to rest on top of the poles during the steep downhill stretches. If the trail is rocky take your hands out of the straps so you don't get the pole stuck in a hole, fall and break your wrist.

Secondly, check your socks. Wearing cotton socks will cause the balls of my feet to hurt. I'd recommend a thick wool sock like Smartwool, or a synthetic like Thorlo. You can buy an inexpensive equivalent at Big R's. I think they are called Ralson. They have an R on the top of the ankle.

It's possible your hiking technique is causing the problem. It's counter-intuitive, but if you lean forward a bit when hiking downhill, it puts your center of gravity over your feet and your feet won't slip inside the shoes like they do if you aren't leaning forward. If your feet want to slip out from under you when hiking downhill, then this may be your problem. Trekking poles will give you the confidence to do this.

If these don't work, try a pair of Danner Combat boots. I like this pair. Danner boots. They are more comfortable than bedroom slippers and don't need breaking in. They transfer the forces differently, and they will reduce some of the slippage in your boot. They also prevent twisting of the foot like you get in shoes. I wear these boots all the time except for short hikes. They are also completely water proof so I usually just walk through shallow streams.

Check your pack weight too. You don't have to go ultralight, but it is possible to stay under 30 pounds for a 3 night/4 day trip with relatively inexpensive gear. Even 25 pounds is not out of the question.

I just noticed you were hiking down the Barr Trail. I've never hiked it, but that is downhill. Maybe just avoid trails that have long stretches of downhill. There are many trails up the road a bit by Seven Falls.

Another thing you can try. If your feet start to hurt after 20 minutes then stop for a 5 minute break after 15 minutes. The rule is rest at about 80% of the time it takes for something to hurt.

There is something else I like to do for fun. Walk slowly for about 100 feet (20 paces counting just the left or right foot), stop for a few seconds and look around. We do this when it's hot because it conserves sweat. It's a great way to attract animals if you don't talk. Deer and elk often come over to see if we want to play.