the 3.5s fix almost all of the problems with the altimas. the 2.5s are utter crap. working at a nissan dealership, there were always 2-3 2.5s a day. i think i have had to actually fix one or two 3.5s in over a year and a half, they are very reliable. there were a good bit of recalls done, make sure to have a nissan dealership check the vin to see if they were all done or not. any kind of engine part for a maxima will fit it too btw, in case you needed something and couldnt find a 3.5 altima laying around. btw 02-03 had the most problems, most of the bugs have been worked out in the later years.