Ticking sound increasing with RPM - lifter problem?

It can be. Lifter noise is tied to the camshaft, which turns at half crank speed, so a lifter tick speeds up as rpm rises. But rod knock also speeds up with rpm — the difference is character and load:

• A lifter tick is light and sharp, from the top of the engine, often most noticeable at idle and sometimes quieter at higher rpm as oil flow increases.
• Rod knock is a deep, heavy knock from the bottom end that gets louder under load (accelerating, climbing hills).

Quick checks to tell a lifter tick from something worse:

• Where it comes from: a lifter tick is up in the valve-cover area; rod knock is deep in the block or oil pan. A long screwdriver (tip on the valve cover, ear on the handle) or a mechanic's stethoscope helps.
• Cold vs hot: lifter ticks are often loudest on a cold start and fade as oil pressure comes up. Rod knock doesn't change much with temperature.
• Load: rod knock gets louder under load and with rpm. A lifter tick is usually most obvious at idle and may quiet down with rpm.
• Kill one cylinder at a time: if the noise drops out when one coil is unplugged, suspect that cylinder's rod bearing. A lifter tick keeps going because the valvetrain still moves.
• Rule out an exhaust leak: a leaking manifold gasket can sound just like a tick, especially cold. Look for soot at the ports.

First things to try for a lifter tick: check the oil level (too low or overfilled — overfilling can aerate the oil and collapse lifters), change the oil and filter with the correct grade, and pull a valve cover to look for anything obviously broken or loose. More: piston slap vs lifter tick vs rod knock.