Just manual stretch bro. I am struggling with length like you and we have same stats tbh.
For me I dont use conventional bundles, I am doing Mandingo Stretch, it is powerful, it is bundle stretch and it is easy to perform and I can hold my dick up to hour in grip. Focus a lot on BTC stretches since they go past your body in "negative" range of motion therefore you get higher stress on ligaments.
Try to support your gripping arm with another arm to intensify stretch (pull stronger), thats what I am doing every time, I dont feel stretch anymore when pulling with one arm I have to use both and it spells magic like goddamn Potter. Dont stress yourself brother. Everytime you get pissed for slow progress, remember brother that there are THOUSANDS of guys with dicks less than 4' who have no clue that PE is possible, YOU KNOW THAT THIS IS POSSIBLE AND YOU ARE BLESSED! You, me, DLD, Mr. Lighting, stillwantmore and thousands of other guys on MoS. Dude we are blessed, maybe sounds sili and pathetic but thats the true...so KEEP CALM AND PULL THAT DICK AWAY BROTHER ???