Car Problem with NORMAL REV. to Speed issue
 

hello hello. so i was wondering if anyone could tell me what could be wrong with my car, the problem im having is that normally while in 6th gear 3k rev my speed on speedometer would be 80mph. that is until today that i did my daily driving on the same road same everything that i do everyday that while driving at 3k rev.. my speed is 75mph. and to get to 80mph i have to pass 3k rev.. i really dont know what the issue is. i dont know what coudl be causing this decrease. if someone with alot more knowledge inform me of what i should check out that would be great
my car is only 2 years old 19800 miles all stock. only upgrade is 18in rims and tires. soo if someone lighten my worries thank you!:sign0085:

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