[Storebror]

there are some problems with the front landing gear

Seen that before but unfortunately cannot find the thread again.
Anyway, this was a known issue for some very early XF-86 mod installations.
I guess you didn't follow the installation instructions precisely. You need either Ultrapack 2.01 or HSFX installed, or you need to download and install the F-86/MiG package at SAS. The F-86J mod relies on those installation and doesn't change anything on them except for the inner wing hardpoints, so we can bar this issue being caused by the J mod.

For me, if the rocket or that bomb on the screen, my game is lagging az hell D:

:?:
I don't really get what you want to tell us here, but rest assured that if you follow the installation instructions, everything will work fine as it did for many many other users before.
One thing which is for sure is that at the moment of impact the nuke bomb will cause lag on low-end systems. That's due to the mass of damaged statics i.e. if you drop the bomb in an area with many static actors around. This particularly comes true with effects mods installed. This is self-evident and cannot be changed, sorry.

Best regards - Mike