Speedometer sync loss

Recently took my 2016 V6 in for 80k service. Had a 3 stage fuel, transmission service and rear differential service. 1 week after services performed took the first hwy drive (generally drive short range trips). After about 70miles while driving apx 30mph in slow peek hour traffic and beginning to accelerate my speedometer guage dropped to ZERO but the digital read out continued. Stop and go fwy traffic the guage attempted to rise a few times but completely off the digital read out by 30mph or so and would continue to fall back to zero as if struggling to function. Took an exit off the fwy and at the first traffic light put it in neutral then back to drive. The speed guage began functioning however it was still significantly off from the digital read out. At the next traffic light I put the truck in park and then on green back into drive. The spd guage then was within 5mph of the digital readout. I drove immediately to Toyota and recorded the 5mph difference as proof something occurred. When the initial problem occurred the truck power felt funny and I was unsure if it was me confused by the chaos of the issue or drop in power. Toyota did diagnostic and found no issues and the speedometers were apx 1mph off eachother but they did find an CAN fault history that they say seemed to have self corrected. Anyone have this issue or a clue what happened, this truck ran amazing before this and now I hear loud tapping noises at idle and while driving. *also noticed that although the service I had performed they were supposed to top off all fluids my brake fluid is very low and my coolant as well. Highly suspect the mechanic fd something up.