I would highly recommend the replacement of Jolteon in the lead position by Vaporeon, who is a far more effective lead. This is not a joke, and I have even used it on a non-Eeveelution team. Here is my preferred set, though there are other item options, requiring a change to hydro pump from surf.
Vaporeon @ Life orb
Modest nature
188def 252spatk 68spe
-Surf
-HP Grass
-Wish/Hydro Pump/Ice beam
-Quick attack
This will beat more or less every lead bar Roserade most of the time. Here is how it fares against some common ones:
Azelf - Surf + quick attack should finish it off.
Swampert - Hp Grass OHKOes easily. This is guarateed unlike Jolteons OHKO
Metagross - You outrun and 2HKO with Surf. Metagross kills Jolteon with Earthquake
Aerodactyl - Surf + quick attack for a guranteed 2HKO. Jolteon is OHKOed by Aerodactyl's Earthquake
Jirachi - Surf 2HKOes, and its attacks do very little.
Roserade - you lose, but you can break its sash with quick attack
Infernape - Easy 2HKO with surf + QA. Jolteon gets 2HKOed by Fake out + Close combat
Tyranitar - surf 2HKOes, and TTar beats Jolteon convincingly
Gliscor - Surf OHKOes
Heatran - Surf OHKOes
Vaporeon is far from useless outside the lead position, with great bulk allowing it to survive its lead matchup with respectable health. Its powerful water move(s) will often deal huge amounts of damage to Vaporeon's electric-type switch-ins such as Magnezone, Scarf Rotom, Jolteon and Electivire, who are all OHKOed most of the time by a LO Hydro Pump. It can also provide wish support to the team, without letting up any offensive momentum.
Good luck