like BJ said it depends on the which runs cleaner. I am betting it would be the silveraldo. The theory behind that is 1 it has stricter guidlines to follow, 2 you have more power and torque to move the jeep,thus making you burn less fuel ,in turn lower emissions. you have to figure the 6 cylender was designed for a lighter vehicle whereas the v8 was for larger. the more power you have the less it takes to move the jeep thus allowing for better everything just about. well as long as you drive by the rules anyway,
Jeep canned that engine claiming they couldn't get it to meet the epa standards.Personnaly I think that is a load of BS. I get alot of new cars in that get worse mpg than my jeep, lexus,mercedes,and bmw to name a few. we all know the power they put out which would seem that they are going backwards.They can get 300+ hp engines to pass emissions why would a little straight six be so difficult.
One thing is for sure you will have to get the computer,wireing,and exaust(complete front to back) to run the engine properly. I know Va was simular in that you couldnt run an older engine in a car due to regulations unless it was pre 74 (I think it was 74) , meaning I cant run any engine pre 89 in my jeep. but if i had a 74 jeep i could run any engine that i wanted too.But if i wanted to run a 97 engine ,i could as long as i retained the proper emissions for that particular engine. Your best bet would be to talk to an inspector and find out for sure. every state is different that is probably why you havent been able to get a straight answer.
