As well as the above, is there any chance that your tyre pressure gauge isn't that accurate?
Just out of interest, what brand of tyres are you using?
I'll throw this one in as an extreme outside chance, but anyway, has the car had uprated springs fitted to the back in the past, to cope with a permanently full boot of rep's gear, whatever that was? ( I must add that I don't know if uprated springs are even available, but these cars often look heavily laden on the back end, even when they're not full of passengers).
The original shockers are Kayaba brand (KYB), made in Spain, if you were looking to replace them (with something else?). The rears should be very quick to change as the suspension spring is not concentric with the shocker, I believe. The fronts are normal strut-type, but the scuttle/wiper trim has to come off to get to the strut mounting nuts, and the securing clips for this which are integral to the plastic trim, break. This is very difficult to prevent unless you are meticulous, and have spotted where they are, and that they are vulnerable! Not a great problem - gravity seems to hold the scuttle trim in place well enough after someone has broken the clips off.
You could also check if your 205/55 x 16 tyres aren't marked on the sidewall as 'XL', for 'extra load'. These tyres have a tougher carcass which can make the tyre slightly less compliant, but some (not Toyota) owners dispute there is a ride difference to be noticed when these are fitted. The load index of the tyre, also on the tyre sidewall, should be a '91', from memory. If that number is higher, then the tyre is designed to support a heavier car, which could have similar results to above, but your tyres having the wrong load index is unlikely, but still worth checking. The XL rating normally goes in hand with the tyre having a 94 load index - basically it is built to be pumped up to a higher safe working pressure than a standard tyre.