Yamaha's seamless shift gearbox has only operated on up shifts since it was first introduced at the Misano round back in September 2013.
Rossi and Lorenzo believe a full seamless shift system will help them combat Honda's RC213V, which excels in braking stability and corner entry.
Both have always believed Honda's full seamless gearbox has given double MotoGP world champion Marc Marquez and HRC teammate Dani Pedrosa a key advantage on corner entry.
Yamaha boss Lin Jarvis has hinted that the full seamless transmission will be available for Rossi and Lorenzo when winter testing resumes back in Sepang on February 23.
Speaking to MCN Jarvis said: "The seamless downshift system is planned to arrive in the near future. And that will certainly help. It will arrive ASAP."
When asked by MCN if the ‘near future' meant Sepang 2, Jarvis said: "I think it should be a realistic scenario. What is important with the gearbox is you can't afford to make mistakes because you are talking about rider safety.
"This is something paramount to Yamaha that whatever we bring we are 100% confident with it."