If that is true the game isnt modeling the P-51 properly. The N should have max range at 2200 miles and the D pony at 2300... which isnt much difference but it is a difference.
A quick look at Dean shows the P-47N with a maximum non-combat range of 2,800 miles. Allowing for warm-up, climb-out, 15 minutes of MIL power and 5 minutes of combat power, the P-47N is rating by the AAF as having a combat radius of 1,000 miles. Under the same criteria, the P-51D is rated with a 700 mile combat radius.
This USAAF table is found on page 600 of America's Hundred Thousand.
And there is this..
"The testing program included determining the maximum range of the fighter. This was done with various combinations of fuel loads and external drop tanks. Ultimately, a test flight was made from Farmingdale to Eglin Field in Florida. The XP-47N took off with two 315 gallon drop tanks hanging from the under-wing hardpoints. Usable fuel in these tanks totaled 600 gallons. Added to the internal fuel load, the N eased off the runway with 1,170 gallons of fuel (usable). At a gross weight of 20,166 lbs., the Thunderbolt headed south in company with a P-47D chase plane. Arriving off the coast, east of Elgin in 3 hours, 44 minutes, the external tanks were dropped. Another P-47D, already waiting at Elgin, took on the N in a mock dogfight that lasted for twenty minutes. The throttle was advanced to military power for 15 minutes of this time, with an additional five minutes in the War Emergency Power (WEP) detent. After these fun and games were concluded the N was turned around and flown back towards Farmingdale. Heavy weather over Long Island caused the plane to divert to Woodbine, New Jersey. Having flown 1,980 miles, total fuel usage was measured at 1,057.5 gallons. There was still more than 112 gallons of usable fuel remaining in the main fuselage tank, enough for another 330 miles @ 1,700 rpm in auto-lean."
Note also that the P-47N sometimes flew with the 165 gallon P-38 drop tanks, as is seen below with a 507th FG P-47N flying out of le Shima in 1945.

My regards,
Widewing