Ok guys, I did some research to see if I could tell apart the years between the '88-'91 LTD (more specifically the fleet version) and here is what I found:

1988-1989: Flat hubcaps as seen here:
http://www.imcdb.org/images/106/808.jpg
1990: First year for the newer style "dog dish" hubcaps as seen here:
http://www.imcdb.org/images/006/685.jpg
1991: "Dog dish" hubcaps still on cars, but 1991 was the only year the front turn signal lenses were clear. I know some of you, including Snookie, have said that 1990 was the first year, but I have checked with some sources and found that the '91 was the only year:
http://www.imcdb.org/images/079/644.jpg

I will be commenting on the appropriate changes for the LTDs on the IMCDb page.