The Cobra 148 must be one of the most 'diddled' with and pontificated about radios in CB history!
You'll find all sorts of nonsense floating about surrounding the circuitry, design and operation of them and usually they've been 'modded' to hell and back or all sorts of unsuccessful repairs performed on them.
In the 'old' days of earlier 19-clickety-click very few had gone through such rigorous 'modding' and most garbled SSB transmission problems stemmed back to poor power supplies or RF coming back down the antenna system basically using it (and you!) as an antenna ground plane.
This usually came with reports of how it works fine in the car (on a 12 volt battery system that can supply umpteen amperes) but doesn't hooked up to the cheapy, few amps, from a CB shop or 'good' mate cheap, rubbish power supply at home....
The RF 'feedback' problem (which won't always show with just a damn SWR meter) was either never resolved or swapping antennas and some 'decent' coax bunged on for good measure "fixed it"..... usually with lengths of 'multiple half waves' coax as suggested by your friendly neighbourhood CB shop making the coax a better 'groundplane' or counterpoise than it was first time around(!)
(Nowadays there's a lot more understanding regards such matters as well as common mode currents.)
Of course there was the good old 'power mic' problems too.....overdriven audio stages on the CB or the internal electronics of such a microphone 'amplifying' the RF feedback problem to the umpteenth degree.
I could as has been done on many occasions provide you with a total 'stab-in-the-dark' guess solution some of which have gone down in CB mythological history such as the "Yeah mate, needs re-capping that does".......that one never gets 'old' apparently.
On the Cobra these 'suggestions' will often revolve around the electrolytic capacitors surrounding the audio chip. Often cited as the "But they're just 10 volt types" never knowing the basic electronic design of audio DC isolation or frequency feedback so will never, ever see the power supply voltage on them during normal operations. (A rare exception noted further down.)
You say that your audio chip has been 'replaced' and I hope with a decent version rather than the el-cheapo Chinese copies that spew from their semiconductor plants. (Mostly 'Asian' actually with the Philippines, Taiwan and Vietnamese plants often incorrectly 'copying' the semiconductor mask or PN diffusion processes!)
If it was then the many guesses at changing resistors or capacitors in it's surrounding circuitry may actually help its poor operation.
If the original chip blew short taking out the power lead fuse then and only then might it be worth checking those '10 Volt caps'.
(How many times has the "yeah, that'll do" bigger amps fuse or silver foil 'temporary' fuse wrap become a permanent fixture?)
That's why 'myths' persist....with a grain of truth or exceptional circumstances.
My best 'guess' for you (as in not having the radio in front of me) is to check that the soldering of the replacement audio chip doesn't resemble some lead lined robotic/terminator seagull/pigeon poop monstrosity. Or that the PCB copper tracks haven't lifted from using Dad's old 1960's plumbers soldering iron.
Or probably the old example where one of those PCB chassis screws tumbled under the table, just out of reach, killing my back so we won't bother or 'mysteriously vanished' cases and never replaced. On some radios the chassis provided ground continuity for the main PCB!!
Get it repaired or bung it on eBay with the 'spares or repairs, no returns' nonsense that abound nowadays. I'm still amazed at the silly prices paid for such items.
Probably not a lot of help and I am known to 'waffle' but there you go.
I could have just left it with the "Yeah, needs re-capping......bung it on the bay".
All the best,