my dakota seems to be fine for a few days, then if i go and do so small trips like 2 miles to work and home a couple of days a week then then when i take my foot off the gas the rpm gauge just buries itself and the truck shuts off and comes back on. Then if i go for a 20 mile plus drive and come home and repeat to work and back for a few days then it starts all over agian. so basically not sure if it's the alternator or the battery??? any help would be cool ....

 

Does it just bog down when it is just started and your sitting still, then it comes back to normal idle rpm?

 

you can have the alternator tested at most parts stores, or you can check it with a multi-meter, but this is harder to do...

 

sounds like you have some type of corrosion building up. might want to take off the cables and give evrything a good wire brushing.. when the battery goes it goes. this is the only power source that will keep the computer running the engine. its not like older cars were you would disconnect the battery and the alternator would keep everything running

 

Agree. Check your cables and terminals for corrosion. Clean 'em up with a little baking soda and water.