ML320 haven't driven in 8 months
 

My Mercedes ML320 has been sitting in driveway for approximately 8 months.
I would start my vehicle periodically.
(Though never drove my ML320)
For the first time the other day I finally drove my vehicle within my community and noticed it appears that I may have a transmission issue??
I would get up to 25\35 miles per hour and it was quite evident it wasn't shifting gears.
(I have never had an issue prior with transmission)
Do you suggest that I have the fluid changed??

Hello and welcome to the forum! I would start there and see if the resolves it self. Were they hard shifts or just pro-longed; meaning that it would sit at a higher rpm for a bit and then finally shift?