Is he an easy keeper? I might start first with getting him slimmed down by cutting back on his feed a little if you can. I am a big fan of free lunging so if you have any place to do that I would. It seems to help my horse with being more motivated. Don't be afraid to get after him just like another horse would, as my trainer tells me, get mean. As for the steering maybe try flexing him on the ground and at a stand still when you're in the saddle. I'm not good enough to flex while moving yet but if you can more power to you.
Also how tall is he? My mare, she's a shorty, has some problems with getting faster. I have to constantly jiggle or move the reins in some way to keep her attention on me. She has a really bad problem of freight training with me when we do anything more than walk. Hope this helps I know I haven't said much.
He's a very easy keeper, he's just lazy. I wish I could but he's fed in a pasture with two other horses. I prefer free lunging myself, but they took down the round pen, so I tried to lunge on a lead line. Not too good. I can flex his head and neck on the ground and even in the saddle when at a stand. However he'll start off jogging then pick up speed and trot into a corner. He's around 15 hands or so.
Here are my thoughts... but of course, without seeing you ride, it's hard to know for sure what's going on.
Issue #1 and Issue #2: Most likely related. Just like people, it's harder to do work when you're overweight. Just slowly work on building up his muscles and reducing his fat, and these will probably get better.
Issue #3: Have you tried a crop to avoid having to nag? I've found often a tap with a crop will wake them up - sometimes just the sound of it is enough to get their attention.
As for rhythm, work to control that with your seat and legs. It'll take time and practice, but the more you do, the better you'll get.
Of course, both of those are for when you're in the saddle. I don't lunge, so I can't help with that.
Issue #4: How are you trying to get him to slow down? If he's throwing his head, it sounds like he's fighting your hands. Try using your seat and legs to ask him to slow down/regulate his rhythm, instead of using your hands.
Issue #5: When I got my horse, he had little steering. Sure, he'd go in the general direction I wanted, but he didn't do straight lines, he didn't do circles, and if we aimed for a point we might come within a few feet of it. If we were lucky.
Three things helped me.
First, starting out with LARGE, very gentle circles, and then working my way smaller over several rides.
Second, doing LOTS of walking all over the place where he had to listen closely to me. Walking figure 8s around barrels, circling jump posts, walking between trees. Anything that didn't involve just following the arena fence. When he got it down walking, it was easier to transfer to the trot.
Third, teaching him to respond to the leg. Once he learned to move off my leg for side passes and leg yields, it became MUCH easier to control where we went, as opposed to relying on the reins.
Good luck. The biggest thing is always patience and consistency. Do you have an instructor to work with?
He's fed in the pasture with two other horses so that's pretty self explanantory, lol.
The owner gave me a crop although I didn't have to use it, I did get some life out of him finally.
They tell me with him I have to pull and release with my hands to get him to slow down. I normally ride with with a lose rein, because most riders there ride with heavy hands. Plus its bad enough when the bit is shoved up their mouths. When I told to shortened them to the length that they wanted, he fights even more and I pretty much expect it.
I am not really sure how to slow him down with my legs and seat, haven't been taught that.
That's a good idea now that I have a crop I can get more lively walks out of him until we work out up to trotting.
Thank you for the tips and suggestions. I can't wait to get started Friday now what I finally have a weekday off.