If chemical engines are continuously being the problem, than why don't we improve upon those?. It's already stated what better engines and reactors will do, more power production and better thrusters, are long term benefits we are going to need for larger ships and cooler and more advanced technologies. We have the advantage, and instead of an attempt at pushing, this is a perfect time for a investment design turn.
Fission-Fragment Engines: A very versatile engine, that also performs the ability to act as a power source. It utilizes the technology of fission and the ability to fragment itself with the integrated nuclear reactor to be able to nearly the triple amount of propulsion and thrust a standard chemical engine can perform. It is also versatile since it has an integrated fission nuclear reactor, allowing it to provide ample amount of energy when compared to our photovoltaic cells.
Probably is the Fission-Fragment Engines (I'm just calling them FFEs, hereafter) spew radioactive particles as they burn. (If that's incorrect, please, let me know) Our ground troops probably would not appreciate this. At all. A gunship would likely need to be of the Warthog/Spook variety and just do flyby runs, or of the rotary blade type that can hover. At least until we get some form of repulsion tech.
I like the Gyrinos, I really do, and I feel they are a tech we should expand on later, but I stand by my earlier concerns about a small vehicle that's still effective on offense, defense, and all-terrain capable.
So I'll throw my own design into the ring...
Margrave APCThe Margrave was born of a very particular need: How to get our current generation of shuttlecraft to carry a combat effective all-terrain vehicle into a combat zone. Instead of using particularly advanced designs in order to create miniaturized combat vehicle, the Margrave uses a clever way to get around the space restrictions imposed by the interior area of a drop shuttle, and are the direct result of one engineer saying "Fuck it all, why don't we just refit the goddamn shuttle?"
In the end the Margrave was (thankfully) not just a refitted shuttle. It's 8 meters long, just shy of 3.5 meters in width (in order to fit a shuttle berth), 3 meters tall, fits 10 (3 crew operators and 7 passengers), and weighs about 20 tons. She's eight wheeled, with a heavy-weight chemical engine capable of pushing her to a decent clip even over rough terrain. The Margrave is amphibious, using a system of twin water jet propellers when swimming. She is, however, rather slow at this.
Armor-wise she's fitted with thick angled plating, quite effective against anti-personnel weapons, and offering modest protection from higher powered weapons. For armaments, in addition to six slide-open firing ports usable by our soldiers, she's fitted with a top mounted dual bolter of enhanced caliber. This weapons is still dumb-fire with course correction, but the larger scale of the missiles as our engineers considering adding tracking in order for the Margrave to provide indirect fire support to forward teams as well as stronger AA.
In order to be launched at a planet like a shuttle, a disposable ablative shell is afixed to the bottom of the vehicle via explosive bolts. This shell covers the comparatively delicate wheels and water jet assembly, and makes it possible for the vehicle to survive atmospheric entry. Unlike a standard shuttle, its increased weight means it deploys all of its chemical thrust fuel as braking thrust, and deploys parachutes once at a reasonable altitude. On the ground, the explosive bolts are detonated in order to free the Margrave from the remains of its reentry sheath and the empty chemical thruster. From there, it's strictly a ground vehicle, and absolutely requires a full transport in order to get back into orbit.
tl;dr:
This beastly fucker, with the ability to be launched not as cargo on an ITC shuttle, but as an one-way transorbital vehicle the size of a shuttle.
It's not light. It might be fast on land, but it's not going to be quick in the water. She's got transport capabilities, and a decent offense/defense combo. She can get to a planet without an upgraded transport, but she can't get off one without help.