The NP 205 is gear driver. I think the 203 is chain driver and the 208 and 241 are chain driven. The 205 has a low ratio 1.96 I think. The 208 is like 2.61 and the 241 is 2.72 The 205 is the strongest and the 203 is pretty strong too. The 208 is aluminum and if it has a skidplate it should be fine if you keep enough oil in it. A 241 is like a 208 but its a little stronger and I thin it has a better lubing system. They started using them in 89-90

90K5

 

90K5 said it right. 205 gear, 203, 208, and 241 are all chain. 203 has steel housing, 205 has cast Iron and the others have alumnium. Obviously 205 is the overall better one, b/c its gear driven, less goes wrong with it and more can go wrong with chain. Normal driving, all is good.
Boss

 

The 203 is full-time, others are not. I've been using a 205 with a 4-speed in an 86 for years and I love it!!! It is the toughest you can find!!

 

203 are cheap and have 50/50 split to front and rear tires none of the others do. however they are full time unleess you up grade. 205 are the strongesst of all but low rang is high. 208 have the best low range but al case. i run 203 behind a 450 hp bbc with 411 and 35 tires and have never had problems.

If it has tits or tires it will give you trouble.

 

Hi all..my first post here..I have recently purchased an 84 Jimmy Sierra Classic,167,000km,3 inch lift and 33 inch tires..I am happy with the truck.My first thing to do is convert to Part time hubs with a locker..can I keep my 203 or should I just go ahead and have a 205 put in aswell..any thoughts appreciated(not overly mechanically inclined here..lol)
thanks.