The Khorramshahr is allegedly related to the North Korean Hwasong-10 IRBM also called the Musudan 4 or BM-25. I'm guessing Iran contributed to the funding and research of the Hwasong-10, among other projects, and therefore reaped the rewards. Others say Iran purchased 18 Hwasong-10 missile sets from North Korea in 2005. Really who knows.
Some sources list the Khorramshahr as having a 1800 kg warheads with a range of 1000-2000
The Hwasong-10 is listed as having a 650-1250 kg warhead with a range of 3000-4000 km
Correct me if I'm mistaken but isn't it less a matter of fuel and more a matter of the size of the warhead which directly effects the range ? I'm assuming some missiles in Iran's arsenal have various sized warheads, with larger warheads reducing the range ?
Assuming a 650 kg conventional warhead at a range of 4000 km, with a decent margin of error, this would make the Khorramshahr more a weapon of terror than anything else. Of course in a city center with skyscrapers, even a dozen such missiles, especially with a submunitions (multiple warheads) can be absolutely devastating. It basically gives Iran the option to say to the Europeans or a potential rival "You bomb my country I'll bomb yours"
In my opinion Iran should stop beating around and bush and just come out with an ICBM or something much beefier than the Khorramshahr. They can still claim the ranger is 2500 KM I suppose.
However I'm guessing that Iran will not publicly display such a weapon since it would definitely help boost the American narrative about Iran being a threat and undermine Iran's efforts to purchase advanced fighter jets and weapons from Russia and China.