Looks like Clematis texensis, perhaps 'Princess Diana'.

Here is a link that might be useful: Clematis 'Princess Diana'

Looks more like a "Duchess of Albany" to me.

I have both. PD is a shade darker pink w 4 petals and DoA is lighter w 6 petals. PD, with EFH parentage, blooms much earlier in my garden

Sir Trevor Lawrence is another possibility, or it may be an unnamed cross with texensis parentage.