Diesel Bombers

I just bought a 1998.5 24 Valve Dodge 2500 4x4 in December.It had 199,000 on it and had 2 other owners.The last owner knew my Uncle and only put 54,000 on it in the 10 years he had it to haul horses.He said lift had been replaced and you can tell he has taken very good care of it.It is totally bone stock(besides lift pump)and I have put 1,500 miles on it and just changed oil and fuel filter the filters I took off both looked pretty good and the old oil was not very dirty but I have the last 10 years maintenance records and it had been a year since previous owner had changed oil because he bought a New 6.7 and it has had oil and fuel filters changed every 6,000 miles.Everything on the truck works as it should Heat,No Cracked Dash and the body is totally straight but paint is faded in spots and clear coat is peeling in spots.I was looking for short bed quad cab that had already been Bombed but the ones around here where either eat up with high miles or ragged out or the body's where in bad shape.So I got extended cab Long bed but I am very pleased with truck and I got a great deal on it.$7,500.Is there anything I need to look for as far as injection pump,Maintenance,Lift Pump or any other suggestions? My cousin has 98.5 Quad shortbed 4x4 with 136,000 he bought 3 months ago and the lift pump went out last week and yesterday he found out it also got injector pump.He paid a lot more for his truck.Any help is appreciated and what is best RPM's to shift and should I not let idle till I get heat like I have been for the last couple of weeks?