MacPro sluggish running Mint Linux 19.3 kernel 5.4.0 vs 4.15.0

I am having some issues with the 5.4.0-62 kernel on my macpro running linux mint 19.3. It runs very sluggish, with windows taking a few second to render, it works fine under 4.15.0-130, i though it may be a driver issue below is the output. Its no a major issue if i stick with 4.15, but support runs out in 2023. This machine is not on all the time as i use it mostly for file storage, backups etc, what are your thoughts on running an old kernel when it is no longer supported, maybe try a new distro (was thinking of lubuntu) or try and find the problem i am having with 5.4.0? 

On a side note the ATI Radeon HD 5770 is a mac version of the card, and the macpro has a wierd 32bit efi/ 64bit CPU i had to fix with Matt Gadient ISO Mod:

https://mattgadient.com/linux-dvd-images-and-how-to-for-32-bit-efi-macs-late-2006-models/

OS: Linux Mint 19.3 Tricia x86_64

Host: MacPro1,1 1.0

CPU: Intel Xeon 5150 (4) @ 2.626GHz

GPU: AMD ATI Radeon HD 5770

Memory: 1040MiB / 16034MiB

Kernel: 4.15.0-130

Graphics:  Device-1: Advanced Micro Devices [AMD/ATI] Juniper XT [Radeon HD 5770] driver: radeon v: kernel 

           Display: x11 server: X.Org 1.19.6 driver: ati,radeon unloaded: fbdev,modesetting,vesa 

           resolution: 1680x1050~60Hz 

           OpenGL: renderer: AMD JUNIPER (DRM 2.50.0 / 4.15.0-130-generic LLVM 10.0.0) v: 3.3 Mesa 20.0.8

Kernel: 5.4.0-62

Graphics:  Device-1: Advanced Micro Devices [AMD/ATI] Juniper XT [Radeon HD 5770] driver: radeon v: kernel 

           Display: server: X.Org 1.19.6 driver: ati,radeon unloaded: fbdev,modesetting,vesa 

           resolution: 1680x1050~60Hz 

           OpenGL: renderer: AMD JUNIPER (DRM 2.50.0 / 5.4.0-62-generic LLVM 10.0.0) v: 3.3 Mesa 20.0.8