Does Trunks ever pretend to be weaker than Vegeta so as not to hurt his pride?
Trunks actually said in the place of the anime you mentioned - when Vegeta battled the perfect Cell - that he surpassed Vegeta's power, but didn't told Vegeta since he didn't want to hurt his pride, he's telling this to Kuririn after being noted that he's been stronger than Vegeta, Trunks tells Kuririn that though Vegeta surpassed the SSJ level, he surpassed even that.

That being said, in his fight against Cell he found out that his level beyond that realm Vegeta could have acquired or maybe has, but didn't made that in the fight against Cell since it forces the user to power up the muscles and by doing that reducing the user speed.