Glad to hear your getting PT advice! Not just gluts, but medial gluts on side of your hips. in the PT clinical setting we do the resisted T-band walks and forward backward resisted steps.Oh neat, i have this too. Apparently it's not wildly uncommon, but i haven't come across anyone else who has it - I suppose not everyone has had such enduring back pain that they've ended up with an xray of their spine!
My PT work echoes the same thing everyone else in this thread has said. Stretch the hip flexors, strengthen the core, also strengthen the glutes (to help stop the pelvis falling into APT) . I have some gentle mobility work as many of my lumbar vertebrae have such tight musculature surrounding them that they're effectively locked in place, causing my spine to "hinge" in certain spots when i bend it. (rather than the whole spine curving) These locked vertebrae should be fixed/relaxed in the long term as a result of the rest of the PT work I'm doing, hopefully.
Also kicks in the 'Multifidus' musculature which is part of your back extensors and a vital part to your 'core'.
This is an advanced way to do them. If your fit you should like the higher level way to do them, if this is too hard don't do the 2nd T-band on the upper thighs.