Don't head down the slippery slope
When I had a 95 Trophy I had the same problem. Check your battery and charging system as if that isn't in good shape the symptoms you describe can appear.
More importantly though, I'd suggest stop paying a lot of money for experimentation. Motorcycle mechanics and electrics is a science, not an art. All too often we visit the dealer and the dealer tries this and that with no good result. After trying a lot of thises and thats, they stumble upong the problem and fix it. By then you've paid lots of money and the $300 reasonable service fee has become nearly a thousand. That is unacceptable. Here is what I did after having had enough of this type of service (not my current dealer-they are great).
Pay for a diagnosis only. For a lot less than trial and error the service fee should isolate the problem. Replacing parts on and on hoping to fix it is not service, a monkey can do that.
When you get the results of the diagnosis, get a quote for the repair and with a statement that this is the solution and if not, no charge.
If the dealer isn't willing to do this, find another dealer, you have found someone incompetent or worse, a rip off artist. I know I'm sounding harsh here but for too long, dealers have just replaced part after part and eventually anyone can fix anything that way. Why do you need them?
Triumphs aren't any harder to work on than anything else. Try to have electrics on a Honda CX Turbo or mid 80s Sabre fixed.
Once I started asking for a diagnosis only and paying for that, things changed. Things went from parts replacements to figuring out what the problem was and fast, reasonably priced solutions.
If new coils didn't fix the problem, the dealer owes you $500 period. I wouldn't give him another penny.
Find yourself a good dealer and talk to them. I delaer shopped when I recently bought my 2000 Trophy. They treat me like Gold. I spend my money there in reasonable amounts for high quality service. When they say the bike will be done, it is done. No surprises on the price because I know ahead of time what it will cost. No fix, no money.
Sorry for the rant but just because it is a Triumph doen't mean it has to costs thousands to maintain and every problem isn't rocket science.