Alternator charging issues

I have a 1994 jeep cherokee sport, 6 cyl. 4.0 liter 200,000 miles. I just changed the alternator after getting it tested and finding out it was bad. Everything things seems OK now (It's cranking normally and the "check engine" light has gone out) the only thing I noticed is that the charging gauge reads 14 when I am driving but when I am idling it is charging at about 11-12. Could it be that the drivebelt is not tight enough? I did not have a guage to measure the tension on the belt which is a serpentine belt. I did however mark the adjustment bolts posiition before I loosened it and I tightened it back to that position. What do you think?


Terry