1HD-T is a simple old, low running, high mileage, reliable, mechanically fueled, controlled and most of all a fuel efficient diesel engine.
12 Valves (2 per Cylinder), Single overhead cam with a long stroke design. It is designed to dish out maximum torque at 1500RPM and maximum power at 3500RPM. Keep in mind the engine's maximum revs are 4000RPM
One should be at 110km/h in 5th gear at roughly 3000RPM. If you 80 does that then there is nothing wrong with it.
Petrol cars have high speed engines which rev upto 7000rpm and their torque is dished out at nearly 4000 RPM. They also weigh half as much as a Cruiser and have longer gear ratios. The 1HD-T dishes out a mere 160hp while torque is astounding at 350 n-m at 1500 RPM.
I say get used to it or swap it for a 1HD-FTE. 
That bugger has the grunt to go upto 180km/h of course with its original automatic transmission.
