Improving metabolic efficiency I'm doing road cycling, on hills, over long distances.

Typically at the moment, I'll do two 30-40 mile evening rides in just under 2 hours. Generally either 50ft per mile climb or 100ft per mile climb. These are fine and even going straight from work, with just water, I'm fine energy wise.

However, Sunday's are long ride days, typically 5-8 hours of cycling over 70-100 miles, typically with 100ft per mile climb ratio or more.

I ride with a guy 5 years older than me with one year more cycling training.

However, he rarely needs to eat on the ride, and he'll manage with a few gels and his energy drink.

Whereas, I'll have chugged 1-2 litres of chocolate milk, four rounds of bread (in the form of peanut butter and jelly sandwiches), a (big) bag of minstrels (yeah, jelly babies are better, but, I loathe them). PLUS the energy drinks and gels.

I've always had 'issues' with blood sugar crashes if I don't eat enough on a regular day. I seem to burn it fast.

What can I do to help re-train my metabolism to work better?

Fitness wise, my RHR is around 54bpm, my MHR is 192 (based on highest garmin logged figure), my BMI is bang on 22. The guy I ride with has an RHR of 46, has peaked his MHR at 199 and is probably (though I've never asked) about right on his BMI too. So yes, the fact I can't hold pace with him is because he has an edge fitnesswise, but we have a 'system' of him not waiting for me when I start to drop on the hills, so he's still setting PRs, but still doesn't need to load the calories like me.

I'm aware that my body stores energy in the form of glycogen in my muscles, and it's this supply that is burned first, followed by converting fat to use or any fast carbs I take in. And I'm eating a good amount of carbs for storing up the energy. Saturday night is typically a big pasta trough and a big bowl of porridge before I ride. The guy I ride with on the other hand is gluten intolerant and not taking pains to carb load. And often turns up hung over too. Just to rub it in :)

My fitness is clearly improving, I'm constantly moving on my PRs etc, however, I'm just not getting more 'efficient'.

Which means I'm carrying more weight in food which won't help me keep the pace will it: ;-)
The problem is burning too much carbs/glycogen and not enough fat, since you body has an essentially unlimited supply of the latter.
How? One step is to eat more fat and less carbs. That trains your body to burn more fat. This article also suggests pushing your limits on how far you can go without eating, as a way to train your body to need less. Another point is that you burn more carbs (vs. fat) at higher levels of effort. Do enough training at low effort, and your body will get used to using fat. That's the idea behind Phil Maffetone's training philosophy.