I am obviously by the sounds of it one of the latest potty trainers ever. My son was 3 years 4 months ( back in March), it was a living hell and still is! Wees were not so bad, infact at first he was more than happy to go frequently for a sticker. Poos took 6 weeks, potty would be right next to him, he'd just poo in his pants (he always went regularly 2 or 3 times a day). So fast forward nearly 4 months, he refuses to go for a wee and holds it for a long as possible, still wetting himself at times and he has learnt to hold the poos until he has his night time nappy on. I thought waiting until he was older and could understand was easier but no he is just really stubborn and if he doesn't want to do something he won't. When he was in nappies he'd frequently say no he hadn't done a poo when he had! Honestly found the whole potty training thing sooooo stressful, it was and still is my worst nightmare!
I would definitely say go cold turkey though, pull ups are too confusing! Only use for night time is best I think!