Prepping pedals when installing
Sounds like you tightened them too tight.
You did everything else right - pedals on the right side, threaded the right way, grease.
So, if you had to use a 6 foot cheater bar you might have used a little too much muscle when tightening.
According to bikeride.com pedals should be torqued to something between 276 and 354 inch pounds or 29 to 40 Newton Meters depending on the crank arm.
Campgnolo = 40 Nm or 354 in lbs
FSA = 29 to 34 NM or 257 to 301 in lbs
Ritchey = 35 Nm or 307 in lbs
Shimano = 35 Nm or 304 in lbs