I noticed the timing belt tensioner I got (part no. 13540 50030) is about an inch shorter than my old one on my 00 gs4.

can someone verify the correct part number? did they change the design of the tensioner? what's the difference or IS there a difference?

thanks

That is the part number shown in the online manual for the 98 GS400. I would just call the Lexus dealer and ask them to confirm the part number.

18 - Tensioner 1354050030