I'm just looking for an explanation

Ive had Forza 5 on XB1 since release and I played it for a while then put it down. I started playing again 6 months ago and I have been disabling assists one by one. At the end of Forza 5 I was using only ABS and normal steering. Since online was pretty much dead, I played rivals. I have top 5% lap times on rivals. Ive had a pretty good start to forza 6, and I race on career with the driver level at highly skilled and I come in 1st place everytime. Heres the problem, I lose and come in dead last everytime I play online. I try tuning myself and I suck. I'm a pretty disciplined racer but my cars always suck. Or perhaps I'm not practicing enough? Im just looking for a forza vet to help out with tuning or just general help.

TLDR; I play Forza alot but lose every race online. Looking for help.