Here is how to year date a 700R4/4L60 transmission. It can also be used to date 4L60E transmissions if you continue the date progression. 4L60E's use the letter D as the 3rd digit of the 3 letter model code, where 700R4/4L60 uses a M. To go into the 4L60E years just go up from the 1993 code, 1994 =4 1995 = 5 etc. Just looked at 98 GM repair manual and 98 and later trans, the 1st number after the 3 letter code will be the build date of the trans. Example- if 8 is the 1st # in code for 98 model year, after the 3 letters could be a 7 or 8 for the build date.