After trying a few different things, I decided the easiest way to deal with my power-to-weight ratio/road speed issue is just to arbitrarily let limits on the speed of walking vehicles. I would estimate the top speed of a Fire Toad to be no more than 30 kph, with a top off-road speed of 18 kph. The vehicle may have enough power to move much faster, but the nature of the design makes higher speeds dangerous and extremely uncomfortable for the driver.
I have also redone the build with a much smaller hull. I realize, after comparing the Fire Toad mini to a human-sized miniature, that it is far smaller than 81 kl. I have decided to go with a displacement of 2 tons, which gives a volume of 27 kl. I also reduced the armour value to 10.
Finally, I have done some interpolation in the beam laser gun table. It is a big jump from 1.0 to 5.0 MW, so I graphed the penetration, range (which is linear) and damage as a function of power and was able to derive values for other power settings. I chose 2.0 MW beam lasers, which have a penetration of 16/3, a damage of 7 and a range of V.Distant (10). This allowed me to use a smaller fusion reactor. So, my final design is as follows:
CraftID: UNA "Fire Toad" small strider TL 10 Cr 967,000
Hull: 2/5, Disp = 2, Config = 4USL, Armour = 10E, Unloaded = 20.8 tons, Loaded = 21.3 tons
Power: 2/2, Fusion = 5.0 MW, Duration = 10/30
Loco: 2/2, Legs (x2), Road = 30 kph, OffRoad = 18 kph
Commo: MaserComm = V.Distant, Radio = Regional
Sensors: Passive EMS = V.Distant, EMM
Off/Def: HardPoints = 1
TL 8 beam laser gun (x2), Pen/Attn = 16/3, Damage = 7, Range = V.Distant (10), Sig = Hi, AutoTgt = 2
Control: Computer = 0/bis x1, Panel = Dynamic link x1, Special = HeadsUp, Environ = basic env, basic ls, enhanced ls
Accomm: Crew = 1 (Operator = 1), Seats = cramped x1
Other: Cargo = 0.5 kl, Fuel = 0.72 kl, ObjSize = Small, EMLevel = Faint