1998 Plymouth Voyager breaks

It sounds like you may have a problem that is totally unrelated to the leaking steel lines. A high and hard brake pedal is often caused by a constricted rubber flex hose, usually to a front wheel. The additional symptom is if you push hard on the brake pedal, then release it, you will force brake fluid to that wheel but then it won't release freely on its own. You may get a thumping, a pull to that side, or it will get real hot.

You can determine if a line is constricted by opening the bleeder screw on the caliper. Brake fluid should dribble out at a pretty good clip. If it doesn't, loosen the cap on the reservoir so no vacuum builds up in it. If little fluid comes out even when a helper pushes on the pedal, look for the steel bracket that is crimped around the middle of the hose. Rust forms inside that crimp and squeezes the hose. Use a large pliers or a large flat-blade screwdriver to open that crimp a little.

Did you bleed the brake system after you install the brake lines?
Point being, if you didn't bleed them, then the brake pedal would still go to the floor. If you didn't bleed them and now the brake pedal is hard, then it is something awry in the hose replacement process. Have the mechanic to recheck his work.

Meanwhile, raise the front wheels of the vehicle, (secure the vehicle on jackstands or vehicle lift), crank the engine and pump the brake pedal about 10 times. With the vehicle still running, try to turn each front wheel by hand to see if they spin freely.
If not, the "stuck" tire is the one with the brake problem.
If they both turn freely, have a partner to apply the brakes, now try turning the wheel by hand. If one tire stills turns, this is the one with the brake problem.

Repeat this "test" on the rear wheels as well.

Post your results here please.