before you embark on further repairs be sure to double check with this forum. what stands out is the fact that your engine temps are around 100 and highway speeds do not bring temps down. that sounds like a busted thermostat to me. on that taped hose - if your mechs really pressure tested it, and it was a pressure bearing hose, they would have found it. if it's the overflow hose that goes into the wheel well, it isn't pressure bearing but there have been reports of elevated temps as a result of that particulat hose. sounds like a good car otherwise - don't give up just yet, but do consult this board!
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"