GQ - cruising revs, manual and auto

My auto GQ does 1650 RPM in overdrive at 100km/h indicated on the speedo, but I know from my GPS that this is really only 95kph.
No idea what it does in 3rd, I just drive it! Love the auto, but because it has relatively long legs I am looking at reducing the low range gearing. Has anyone done this in a GQ, and how much would it cost?

My 4.2 diesel 5 speed cruises on 110 doing 2800 rpm. Having larger wheels would effectively be the same as having taller gears, lowering the rpm at highway speeds but also making low range taller.

My 92 petrol efi GQ auto with 265/75/R16 tyres sits on 1750 rpm at 100 kmh in 4th with the torque convertor locked up. In third gear with the torque convertor unlocked it sits on 2600 rpm and with the torque convertor manually locked it sits around 2450-2500 rpm.
Regards Andrew.

94 GQ Diesel auto with 15" rims does about 1950 at 100km/h in 4th

Can't remember 3rd but probably 2800ish

Thanks for the replies folks. Anyone have rpm figures for a manual at 100km/h (both in 4th gear and o/d)? Are deisel and petrol the same. Cheers.

maual GQ 4.2 diesal 2450 at 100ks in 5th 2800 in 4th. 15inch wheels. Get about 12l/100 and 14-15 towing c/t. 360,000ks on clock. Col

Thanks so much for replies. A related question: assuming that 4th gear on a GQ auto and 5th gear on a manual are overdrive, is 3rd gear on a GQ auto and 4th gear on a manual straight through the box (ie, flywheel rpm = drive shaft rpm)? The reason for these questions is that I want to purchase a GQ as a tow vehicle and wish to clarify the differences between auto and manual.
regards, Rob.