Frustrating 300TE Runability

[350SL4spd]

We have always had a warm start problem in our 1991 300TE. Never really bad, but just irritating. It always seemed like a loss of fuel pressure or something, you had to rev it pretty high to get it hold then it was fine, not even rough at idle. We have chased down all kinds of leads over the years replacing cap/rotor/wires/plugs, Temp sending unit, OVP, Valve guide seals, head job, hydro-electric actuator valve. Now the odd thing is that the only thing that solved the problem was changing the injectors. But this only worked for about two months, then the warm start issue returned, but we lived w/ it for almost a year. Now things have declined to the point that it is really hard to start and is real *****y (burbling and missing even backfiring once or twice) up to 15-20mph, then ok, but a little sluggish after that.
My question is what is going on with the injectors? Why did replacing them fix the problem only to have it return after a few months? (And not very many miles in that time...only 101k mi total, so she hasn't been driven to death, but still gets her share of highway time)
I have her torn apart right now. She will get a new fuel filter and I will intensly inspect the injectors, but I don't know what I hope to find. Ilove the car but I can certainly not afford to put in injectors every two months!
Thanks in advance all!
-Matt-