Depending on your Mod Status, and it may not be viable for certain aircraft, it is possible to go from P2/T2 to P2+/T2+ which is effectively the same as a T2i or P2i. SB 71-033 covers the requirements, but essentially you need to have:
Titanium torque strut assy (which all should have anyway)
L623M1003 mast (reinforced) i.e. the one without the integral drive lugs.
EURO 4 or 5 MMI
Main XMSN S/No. 0301 or higher with Transmax oil
Upgraded X-Y fittings
ADC 2
Then you have to change the CAD and VEMD and retrofit the Cat A Switch to High Nr system which effectively means when you have High Nr (Cat A) selected the RRPM will decrease through 55 knots as the ADC is communicating with the FADECS and increase slowing through 50 knots.
Then you get:
AEO TOP from 2 x 75 to 2 x 78
AEO transient from 2 x 80 to 2 x 82
OEI MCP from 1 x 86 to 1 x 89.5
Some component lives are also reduced but not drastically.
Our ship complies with all the above except the X-Y fitting change and have been told that the upgrade and exchange to the CAD and VEMD will EURO 130K!!!!!!!!!!!!!!! and not available for another 6 months. I guess that protects the new sales.
As Ian states the increase in range may be the increase in gross weight available but only if you depart at gross with less than full fuel obviously.
Aircraft after S/No. 249 have a slightly increased usable fuel as they removed a few parts and reconfigured the tank arrangement. This was primarily brought on by certain aircarft not meeting military contract spec requirements and a little hiccup between pre and production aircraft.
Incidentally you can also convert a T2 to a P2.