What kind of trouble are you having? Chipped inserts, I presume?
Which lathe do you have, and does it have a C axis interpolation and live tools? I'm thinking thread milling might be the next-best option, though I'm pretty confident I could help you solve the trouble with single point threading.
You should be using a lay-down style threading bar and insert, probably a Valenite 08IR18 grade VC942. The bar would be SIR 0265 K08 (if no internal coolant) or a SIR 0265 K08CB (carbide, with coolant thru). Those are 5/16 inch size bars, with minimum .310 bore range. You might do best going with the solid carbide bar even if you don't have through coolant.
Single point threading would give you the longer tool life, rigid tapping the shortest cycle time. Choose the right tap for the job if that's the way you go, and understand there will be more burrs. Thread milling will take the longest, but give you the nicest-looking burr-free thread. Full-form inserts are the compromise between the two other methods.