I would say mix up your workout and be vigilent on your calories. Breaking a plateau usually means that your body has adapted to your workout. You can break this by cross-training (try to mix in some workouts during your week where you're riding bike or doing the elliptical instead of just running). This will make your body stronger, too. I'd definitely mix in one interval session a week. If you're running 4 miles, you can probably swing a short HIIT session. But I wouldn't automatically switch to all HIIT (this puts undue stress on your joints and will destroy the long-distance running you've put a lot into). There are a lot of people on this board that think it's the cure-all to everything.
If you're upping your mileage, I'd choose one day of the week to do a long run, then do variations of this during the week. I have gotten the best results from one long run, one medium run, and one short interval a week. Other days should be cross-training (if you want extra cardio) so you don't hurt your body.
Keep with the weights. Every pound you gain in muscle burns another 50 calories. However, I might see if you're doing split weights (arms one day, legs another, for example), or if you're doing a full-body workout. If you're doing one, do the other for a month or so. You may see much better gains mixing it up this way. I'd also alternate lean and mass-building cycles. I usually work 6 week cycles of each, alternating. On the mass-building cycles, I'm sprinting more and lifting lower reps of higher weights. I'm also more specific to muscle group. On lean cycles, I do a lot of long cardio activity and the same weight with higher reps (if you've made strength gains in 6 weeks, you can probably use the same weights you used for your gaining cycle), working a "circuit" training style, where I move from one activity to the other, changing muscle groups, but keeping my body moving the entire time. During your gaining cycles, you should do cardio after your weights, during your leaning cycles, cardio should come first. Since you've been running a lot, I'd start with a gaining cycle (keep in one long run to maintain your distance).
You might try fasted cardio as a way to break the cycle, though I think it will be difficult for workouts where you run 4+ miles. The idea is not to make yourself weak, but to draw your energy from another source. You might try this on shorter, sprinting days.
An example of a gaining schedule:
M: Back/Lats/Abs followed by 20 min. HIIT
T: Shoulders (if you're using the right form, they shouldn't be tired from Mon.)/Biceps/Triceps/Legs
W: Interval/medium cardio day (45 min. cardio at medium intensity or 45 minutes regular intervals)
Th: Back/Lats/Abs
Fri: Shoulders/Biceps/Triceps/Legs
Saturday: Long Run
Sunday: off
Some people prefer different pairings for muscle groups, and that's fine.
An example of a leaning schedule:
M: 30 min. medium intensity cardio, followed by 45 min-1 hour full-body circuit training.
T: 1.5 hour, low-intensity (long walk) cardio.
W: full-body circuit training followed by 30 min. medium intensity cardio
Th: off
Fri: cross-training cardio (biking, elliptical), 1 hr.
Saturday: 1 hour full-body circuit training. Later in day: your choice of cardio.
Sunday: Long run
Good luck to you!
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