Volvo S80 dies or goes limp

Hi! I have a 2004 Volvo S80 AWD. Over the past year or so it will intermittently pull some pretty strange problems out on me. Mind you if I don’t drive the car for a few days they go away. One of the problems is I will go to start the car and it will turn over and fully start then just completely die and my check engine light will come on and it will also say the transmission needs service. This seems to happen randomly and if I get out of the car, lock it, remotely set off the alarm, then unlock and try again. It will normally start and drive fine. Nothing is wrong with my transmission according to the dealership.
Also, when I’m driving occasionally, the car will enter limp mode. My speedometer and odometer will stop working. My a/c will turn off, my mileage disappears and after a while though sometimes immediately it will no longer shift into higher gears.(The car is automatic.) most importantly it will say that my abs is offline and “brake failure, stop safely” will appear. I have taken it to the dealership and they have replaced my abs module. Yet this still continues. I have also had my a/c fan motor replaced in the past, when it wouldn’t turn off even with the car off which drained my battery (so the car has a brand new one) however that problem has been fixed.
Any ideas?!?
Thanks so much

I think you may have a problem with the security system that disables the start. The car has a system called Electronic Immobilizer to kill the engine. It also has an anti-theft alarm. I think your problem is the Immobilizer. As far a the Limp Mode, a faulty Vehicle Speed sensor could cause you Speedometer and other problems.