The Italian, who tasted the top step for the first time in a Renault last year, finished second with the two-race (Monte-Carlo) spec V10 at Barcelona.
But, nonetheless, he sensed a problem with the Toyota powerplant.
Even though Monaco is not tough on engines, Trulli noted that his Toyota - which spewed fire in one pitstop - 'was not too strong' in Spain on Sunday.
"My speeds were not as good as (teammate) Ralf's," JT added.
Even so, Trulli has an eye on the glitzy Principality, and noted that the driver can mean the difference between a good result and - maybe - a win.
He said: "I'll be giving it 110 per cent, you can be sure!" -GMM