Take it to a mechanic. You described conditions... diagnosis is a hands-on thing, and will be necessary, as there is more than one possible cause for the conditions you describe.
Yes, you need to replace the VSS.
The s3 light coulb be your speedometer cable if it is not working mine did that i hope this works.
get it service.
You could be low on transmission fluid. The same thing happened to me.
The VSS (vehicle speed sensor) may be at fault.
Transmission Flush help my Ford! Same issue here.
"I have a Mirage 94. When it gets hot, the transmission slips."
You probably have a slipping clutch band in your transmission. Take it to a transmission shop.
When the cold transmission slips when shifting in the second gear, it means that either the fluid level is not correct or the filters are faulty. When this happens, your gearbox may need extensive repair or may need replacement.
Low transmission fluid and/or fluid leak.
As it heats up, it slips more.
start by checking the transmission fluid level when the vehicle is at normal operating temp