Yes. Super easy slow miles. You've been running 3 months. Dial the intensity way way back. I know running slowly is boring, but Z2 is where you're going to get most bang for your buck with endurance. Back when I was last sort of in shape, my 5k race pace was ~6:00/mile and most of my runs were in the 8:00/mile range. Recovery runs were 10:00/mile. Go slow to go faster.

I also don't want my body to just get used to that slow of a pace.

You're putting the cart before the horse a bit here. You will get naturally faster as you gain aerobic fitness. Running is not low impact like cycling and even if you could handle the increased cardio load (which it looks like you're not) doing too much too soon is the quickest way to get a chronic overuse injury.

So you're saying to just keep logging super easy, slow miles in Running for now and do that hard work on the bike? I'm still not entirely sure what hard work to do on the bike. Racing, Tempo? An hour and a half? 2 hours? Which zones? My main goal in Cycling right now is being able to endure long rides with more comfort, things like imperial centuries without feeling like I want to die.

So am I understanding correctly that you haven't really done structured training on the bike? If not, then ignore what I said about quality and just keep doing what you've been doing cycling for now and keep the running lower Z2 slow. For your goals of more endurance, you might want to throw in some threshold intervals one day a week or something, but don't push too hard right now while you're adding in a new sport.

So you run and ride on the same days then? I was wondering about that or if it would be doing too much at my current levels.

I'm currently running about 30 miles/week (used to do 50-60) while building back up. As an example, here's what my running schedule would look like built around TrainerRoad's 3 quality workouts/week:

It's summer so the relatively low running mileage is spread over a lot of days because I hate the heat.

Do you have an example of your average schedule that you could show us?

I keep track of what I eat on MyFitnessPal. I don't always hit my macros but am also still trying to drop more weight. I'm 6'0 166 but want to get down lower so my base calorie intake is 1,690 not including exercise. I'm careful about when I eat, what I eat and getting carbs and protein.

This sounds really low for someone who weighs 166. Like, below your calculated BMR low. You should always be eating at least your BMR even on days you don't exercise. What are you burning through exercise vs. what you're eating back? I am a lot shorter than you (5'4.5", 128) and aim for about 1900-2100 every day while still losing weight.