I just purchased a 2001 G.V. 1 day ago. I noticed that at speeds in excess of 55mph (100kph) the handling is horrific. I have to strugle to keep it between the lines.(especialy in ruts and on any slightly uneven pavement) This can't be normal, is it     (tire pressure is fine)

I would look at tire pressures, and
the condition, as well as get it alligned

Id bet the air pressure is too low. I would also check the allignment.

Mike

(tire pressure is fine)

When you say fine, what do you have it set at? Having them too high can cause this to happen as well as too low, or uneven pressure(these trucks don't run 34/35psi). However, an alignment is my guess as well.... I'd find a nice smooth road, driving straight, and let go of the wheel - it should track straight, if it's wandering left and/or right, check your alignment. I know alignments are pretty complex, but I've had good luck checking mine a few times with a measuring tape and a helper, by measuring the front and rear of the wheel using the tread line as something to measure from, again, this isn't acurate, but if it's out a lot, it will measure more in the front or back.

In addition to whats already been mentioned I'd jack it up and check for play in the wheel bearings and suspension. Also check the condition of the shocks and struts.

Thanks for all the info guy's!