Yes, that's a 1987/1988 decal scheme. That two tone, tube based, paint scheme was definitely used in 1987. I don't have any known samples of 1988 Sport DLX to verify the paint but I know that the 1988 LeMans models used two-tone fade paint schemes. I suspect the the Sport DLX was probably the same, which would make your bicycle a 1987 model. To corroborate this, you could examine the component date codes using the info on the components page of the Vintage-Trek website. Don't forget that component model year manufacturing pre-dates the calendar year by about 3-4 months (i.e. components manufactured in Sepetember - December 1987 would actually be 1988 components). Good luck.