Exercising the Truth (AKA Grinding, part 2!) Lot's of b***hing on the boards about this one: you have to walk/run for 5 game-miles. You have to be wearing the robes and you have to stay in the desert, on foot. People have suggested using a rubber band on the controller and doing something else, but some folks have been hit by cars or eaten by mountain lions. I don't know how long this will take, but I'll time it.
I ran nearly the whole time (very handy to have Michael's Stamina stat maxed out first) and it took 32 minutes, 14 seconds. I found an area off the road but near a parked car and ran in circles while holding the "X" button down. It made a Spirograph-like pattern with his footprints in the sand. I used a headphone cord wrapped around the left stick and held by my thumb on the "X" button. You'll get a phone call from Cris, the Epsilon leader, at mile 4.0 but you can ignore it to save time.
If you want, you could walk (slowly) in Stealth mode for a mile or so and max-out that stat as well. Doing so will add considerably to the time it takes and the growing arthritis in your thumb(s).
Unknowing the Truth Here is where you have the chance for a big payoff! You must have at least $50,000 in Michael's bank account and wear the robes to start. You have three options: A) Do what they say, give them the $50,000 and you get a rusty antique tractor. B) Drive away from the convoy, lose the security guards like you would a police wanted level and get about $2 million C) Drive with the convoy and when you arrive at the helicopter kill EVERYONE. Then get away with the money and a Gold-level finish.
I really tried to get option C but the helicopter took off every time before I could execute the pilot. Maybe if I had a rocket-launcher I could have gotten a Gold. Anyway, the ground units are easy to ditch, but the helicopter sticks to you better than police helis do. Rather than shoot the security guys and alert the police, I suggest you floor it drive past the helicopter and down the alley opposite the driveway then drive around until you ditch the ground security. Once they're gone look for the freeway tunnel on the west side of the city and the chopper will lose you and you just got 2.1 million dollars to roll around in. Cris will call you but he can shove it. Save your vehicle as it's a "special" one-time car with a KIFFLOM license plate.
Your time with Epsilon is not over. Marnie will text you and tell you to go look for the Tracts. There are only 10, but one will need scuba gear to collect. If you don't have it already, go purchase the Sonar Collections Dock property for the submarine with built-in scuba gear. The observation platform on top of Mt. Chiliad has one but there's another one within 50 feet of it. Marnie will give you clues of where to find them. There's no reward for these, no requirement for 100% completion, no real point, but if you like GTA scavenger hunts, it's the shortest one in the game.