DVM and eliminate that issue. Without doing that you are just guessing. You may have a problem but then your DVM might just be giving false reading in the lower ranges. I would also check the diameters of your old and new pulleys. A wrong size will run the alternator either way too fast or slow. I fell into that trap because when my old alternator died on me I was traveling with two other boats and needed to get my spare one on in a hurry. I neglected to notice that the two pulleys were not the same and ended up burning up my new spare alternator. It didn't fail due to the load but due to over speed. The damn thing just melted from being turned about 3 times as fast as it was suppose to. Boy, did I feel stupid when I figured that one out. I bought a new spare prior to leaving and put in spare parts. Two years later when I needed it I didn't have time to really look at it or spend any time thinking about the job, what caused the original one to fail or what needed to be done during the new install. I just plugged it in and took off. It took about three weeks for it to cook. What a bummer...