Use peasants for garrisons if you aren't already. They are cheap and numerous, so they'll free up good troops for use in battle. You're already powerful, so adopt a policy of extermination in the roman cities you take. That'll cut the numbers way down so you won't need loads of troops to maintain order there. Attrition should be your friend here. You're bigger than they are, so destroy their armies when you can. Try to catch small armies alone when possible so they don't join together. Put forts in mountain passes or at river crossings, if there are any between you and the enemy. Build a navy for use against the Scipiones. Don't spread it out, but keep it all in one fleet. If you hold all of Italy, they'll only be able to come at you by sea or from the north side of the peninsula. Keep the generals out of the fighting as much as possible. Use bribery if you have the spare cash. Since they are also roman, all the troops you bribe will join your forces except for the gladiators. You weaken them and strengthen yourself in one move.